Up to June 23rd , 2020, 55 BeiDou satellites     1     (send) up，meaning the completion of China's self-developed BeiDou Navigation(导航) Satellite System (BDS). BDS appears later     2     America's GPS, Russia's GLONASS and EU's Galileo, but it can match them. As one of the fourth     3     (globe) navigation satellite systems, BDS involves efforts of over 400 agencies and 300,000 research personnel and technicians.

Originally     4     (plan) in the 1980s, the network represents a milestone in China's space effort. BDS is comparable to GPS in terms of the     5     (accurate) of positioning. It also offers short message communication and thus can provide emergency communications in areas     6     conventional communication signals are poor.     7     an effort to improve the quality of their positioning services, Apple and Samsung phones, among others, are already using BDS's signals, and so     8     (be) every Chinese brand.

The construction of complete BDS is a huge technical achievement for China and can     9     (easy) pay off in the near future. Meanwhile, BDS's great contribution to     10     (promote) the world's economic and social development as well as the peaceful use of space has attracted the world's attention.

Many of the Earth’s plants and animals have already died out, and a hundred species become     1     (endanger) every day. If nothing is done, we may find ourselves alone on Earth.

The population of wildlife species has dropped     2     (main) due to the loss of habitats. The forests that wild animals live in are being destroyed by people. As       3     result, their living area has become smaller and smaller,     4     leads to the shortage of food. Besides, many animals are dying out because of all kinds of pollution     5    (cause) by humans in the process of the     6    (develop) of society. At the same time, man is killing off animals just for     7    (get) their fur, teeth and meat.

I suggest that measures should be taken     8    (protect) wildlife. The government should keep people     9    destroying forests and shut down the factories that pollute rivers and air. I think more wildlife     10    (reserve) should also be built. In this way, we can save more wildlife species and make the world a better place.

Scientists often compare coral reefs to underwater rainforests, yet unlike the leafy plant base of a forest, corals are animals.The soft organs inside the hard parts of corals are naturally transparent and get    1    (they) famously brilliant color from algae(藻类）living inside them.

When corals experience stress from hot temperatures or     2     (pollute),they end their interdependent relationship with this algae,typically forcing them out     3    turning white, though one recent study indicates some corals turn a bright neon color when stressed.Corals are still alive when they bleach(白化），but they're     4     risk-essentially immunocompromised(免疫功能低下）－and many     5     (eventual) starve and die, turning a dark brown.

People first noticed coral bleaching events in the 1980s.The problem worsened in 2016, when an El Nino weather pattern,     6    causes warmer waters in the Pacific Ocean,     7    （mix) with an already unseasonably warm ocean and killed off a third of the corals on the Great Barrier Reef.Since then, roughly half the corals on Australia's famous reefs     8    （die) in following bleaching events, risking an underwater landscape 1,500 miles long.

Scientists around the world are looking for all kinds of ways to protect and maybe even revive corals.One option is     9     (create) more marine protected areas-essentially national parks in the ocean.Scientists say creating marine shelter, where fishing, mining,and recreating are off limits, makes the reefs     10     (healthy), and so much stronger.

The palace of Fine Arts was one of the 10 palaces built in 1915 for the Panama-Pacific international Expo. Set within a park, the Roman-style architecture     1     (draw) many tourists, especially wedding parties     2     use it as a background for their photos.     3     sitting on a bench or lying on a blanket on the grass, picnicking is possible. But you’ll have to share your space     4     those who live there,     5     (include) ducks, seagulls, pigeons, and swans. Even from a short distance away from the palace     6     (it), you’ll be able to see its tall columns and round tower that look like nothing else in the city.     7     (locate) on 17 acres at 3301 Lyon Street in San Francisco, the place is within     8     (walk) distance to the former military base of the Presidio. Oddly enough, during World War Ⅱ, The U.S Army used the palace to store military trucks and jeeps. On 1994, the Presidio     9     (transform) to the National Park Service, which made the final chapter in the area’s use as a military facility.     10     the happy tourists seem to appreciate is really worth!

The Amazon rainforest, as the largest rainforest in the world, plays a significant role in maintaining the fine balance of the Earth's ecosystem.

The Amazon rainforest crosses into eight countries, including Brazil, Peru and one overseas region of France.     1     an area of around 6 million square kilometres, the Amazon rainforest is more than half     2     size of China. The Amazon River, from     3     the rainforest gets its name, is close to 6, 400 kilometres in     4     (long). On its journey from the mountains to the ocean, the river supports many different ecosystems. They give this area the richest biodiversity on the Earth: one in ten     5     (know)species in the world can be found here.

More than 1,300 species of birds and over 400 species of mammals hide among the jungle's plant life. The jaguar is one example.     6     a significant number of jaguars survive here, they are only one element of this forest's food chain. They feed on at least 87 species, including frogs. These frogs, in turn, feed on insects which eat     7     (leaf) and fruit.

The Amazon rainforest breathes life into the planet by fixing carbon and producing over 20 per cent of all the Earth's oxygen. Thus, it is often called the "lungs of the planet". Moreover, the Amazon rainforest is a treasure house of species that     8     (use)for food or medicine. Yet there is one major danger to these irreplaceable plants and animals: us. As the impact of human activities grows     9     (rapid), we are left with a question: can we afford     10     (damage) the "lungs of the planet"?