Unlike fossil-fuel power plants, solar and wind power plants only generate electricity when the sun shines and the wind blows. Now the batteries     1     (need) to store power for the cloudy day arise. However, they are still not cheap enough or able to store power for long enough periods     2     (rely)heavily on. A breakthrough in battery technology is of great practical     3     (worthy)for solar and wind energy to become the main part of electric grids (电网). Geothermal (地热地) energy, however, does not require battery storage to ensure a reliable supply and     4     (have)enormous potential instead.

The U. S. leads the world in the process     5     the heat is mined from Earth’s crust (地壳) to produce electricity.     6     it accounts for only 0.4 percent of total U. S. electricity production, the technology could someday provide almost limitless amounts of power. Geothermal power plants situated near hot spots in Earth’s crust could get the intense heat and steam     7     drilling down 1 or 2 miles. The geothermal company Alta Rock Energy estimates that     8     (approximate) 0.1percent of the heat content of Earth could supply humanity’s total energy needs for 2 million years. “Jamie Beard, who runs the Geothermal Entrepreneurship Organization, ranked among the     9     (high)at the University of Texas at Austin, called     10     an “engineering problem that, when solved, solves energy.”

Lijiang was made a World Heritage Site by UNESCO in 1997 for its historic town site, architecture and ancient water-supply system.

The Old Town of Lijiang,     1     (locate) in China’s Yunan province, is one of the last ancient towns that survive in China. Lying in     2     broad, fertile valley in the northwest of Yunan Province, Lijiang     3     (be) a commercial, cultural and political center of the Naxi (纳西族) people since Yuan Dynasty. Lijiang may leave an     4    (impress) on you for its beauty. The aging wooden buildings decorated with red lanterns and local musicians     5     (play) their old Naxi instruments in the time-worn streets show a lifestyle and culture that seem lost in time.

As UNESCO describes the village on its website, “The old Town of Lijiang,     6     is perfectly adapted to the uneven land form, has kept a historic townscape of high quality.” Its architecture is well known     7     combining the elements from several ancient cultures. Lijiang also possesses     8     we call the ancient water-supply system that still functions     9     (effective) today. However, with more and more tourists pouring in, it remains     10     (see) whether Lijiang can continue to keep its traditional lifestyle and culture.

Mount Vesuvius is an active volcano located just east of Naples, Italy. It is the only volcano on the continent of Europe that     1     (erupt) in the last one hundred years, though other volcanoes have erupted on islands in the Mediterranean Sea. Vesuvius's earliest     2     (record) eruption is now its most famous. In the year A. D. 79,     3     little or no warning, Vesuvius erupted and completely buried the ancient city of Pompeii. For two days the mountain shot     4     (volcano) material into the air, spreading     5     blanket of ash over the landscape. Pompeii, located seven kilometers from the volcano,     6     (bury) under five meters of ash. The destruction was so complete that it was not until sixteen hundred years later     7     the city was discovered. Evidence of the religion, culture, and everyday life of the Pompeiians, all     8     (leave) behind in the sudden panic of the volcano's catastrophe, are     9     (remarkable) well preserved. And everywhere there are     10     (remind) of its sudden eruption and the shadow of Vesuvius. Even the forms of the citizens remain. Their bodies lie much as they did on the day of their death almost twenty centuries ago.