Blue whales are the largest animals in the world. But they’re shy, and they live in some of the most remote places on     1     planet, so it is hard for us     2    (see)them. Yet researchers recently found a new group of them. They didn’t     3    (actual)see any of the whales. Instead, they heard their “songs” in recordings made over the last couple of decades. They sped up the recordings to make the “songs” easier to hear.

Each population of blue whales has its own unique songs. The songs can travel     4    (hundred)of miles.

Researchers reviewed recordings made by a network of underwater microphones. The network listens for proof of nuclear-bomb (核弹)tests. But it also records other undersea sounds,     5    (include)whale “songs”.

The researchers found a song that no one had heard before. It includes three parts,     6    (last)a total of about three minutes. They called it the “Chagos” song because it came from around the Chagos Islands in the Indian Ocean. It    7    (hear)as far away as Australia, though, indicating that the whales cover a large range.

The song is similar to    8     produced by several populations of pygmy (非常小的)blue whales. They’re the    9     (small)of all blue whales-about 80 feet long. The researchers said that the new song was produced by an undiscovered population of pygmy blue whales.

No one knows the number of the whales,     10     the recordings provide proof that a new population of hidden giants (巨兽)is swimming through the Indian Ocean.

There was once a town in the heart of America where all life seemed to live in harmony with its     1     (surrounding). The town was surrounded by prosperous farms, with fields of grain and hillsides of orchards. Even in winter the roadsides were places of beauty, where countless birds came to feed     2     the berries. The countryside was famous for its rich bird life, and people traveled from great distances     3     (observe) them. Others came to fish the streams,     4     flowed clear and cold out of the hills.

Then everything began to change: mysterious illnesses swept the flocks of chickens; the cattle and sheep sickened and died. Everywhere was     5     shadow of death. There was a strange silence. The few birds     6     (see) anywhere were unhealthy. It was a spring without voices. Only silence     7     (lie) over the fields and woods. Even the streams were now lifeless. People no longer visited them,     8     all the fish had died.

No black magic, no enemy action had silenced the rebirth of new life in this stricken world. The people had done it     9     (them).

In fact, this town does not actually exist. I know of no community that has experienced all the things I describe. Yet every one of these disasters has actually happened somewhere. A dangerous threat has crept upon us almost unnoticed, and this imagined tragedy may     10     (easy) become a terrible reality we all shall know.

There is little doubt     1     Earth is getting warmer and warmer. In 2013, a lot of people     2     (shock)by a news photo of a dead polar bear     3     appeared to have starved and died. This     4     (alarm) case showed how the increase in temperature had     5     impact on Earth's ecology.

Then what is causing the increase in the global average surface temperature? Climate scientists think the climate process “greenhouse effect” makes it possible for Earth     6     (sustain) life. However, the “man-made” greenhouse effect makes more heat energy     7     (trap) in the atmosphere and causes Earth's surface temperature to rise quickly.

The rise in temperature has led to an increase in extreme weather and natural     8     (disaster) worldwide. News reports are     9     (frequent)broadcast about extreme rainstorms and heatwaves. This requires the attention of people all over the world.     10     is also our responsibility to seize every opportunity to educate everyone about global warming.

Recycling plays     1     major role in fighting against pollution. By recycling paper, we not only save our trees, but we also recycle glass bottles, milk cartons and plastics. It is known to all     2     recycling preserves many non-renewable resources and reduces greenhouse gas emissions. Now cleaners send     3     (little) household waste to landfill sites than before and less energy is required when we are making new materials from old ones.

Health regulations once prevented recycled plastics from     4     (make) use of to make food containers but new technology has seen this ban lifted in some countries.

Rain water     5     (collect) from roads and roofs of buildings is also recycled. Water treatment plants treat    6    (million) of liters a day, removing bacteria and something unwanted. The recycled water cannot be drunk     7    can be used to wash cars, water trees and fight fires, etc. This     8     (mean) there is a reduced demand on drinking water supplies.

New technology is     9     (constant) improving recycling techniques in Europe, America and Japan, but countries with small populations may find that these new techniques are so expensive that they cannot     10     (put) into use in the immediate future.