Scientists sent ............ expedition to ............ Mars during .......... 1990s. 

Air pollution, together with littering, are causing many problems in our large, industrial cities today.

The Aardvark is a mammal that burrows into the ground to catches ants and termites

In spite of her physician handicaps, Helen Keller graduated from Radcliffe with honors

As you come to each town, however small, you will see a sign which states the name of the town and how many inhabitants does it have.

The wooden fence surrounded the factory is beginning to fall down because of the rain.

Some of us have to study their lessons more carefully if we expect to pass this examination.

Afterwards I’d read the manual, I found I could use the computer easily

There exists more than 2,600 different varieties of palm trees, with varying flowers, leaves, and fruits.

Under the crust of the Earth are bubbling hot liquids that sometime rise to the surface.

A telephone, a satellite TV, a fridge and the other facilities are available in our hotel rooms.

That it is believed that most of the earthquakes in the word occur near the youngest mountain ranges – the Himalayas, the Andes, and the Sierra Nevada.

Before she moved to California, with its much milder climate, Betty found that her health improved considerably.

After the team of geologists had drawn diagrams in their notebooks and wrote explanations of the formations which they had observed, they turned to their camp-side to compare notes.

Gold, silver, and copper coins are often alloyed whit harder metals to make them hard as enough to withstand wear.

There is evidence that the caribou originated into North America and crossed over all land bridge into Asia and evolved into the Old World’s reindeer.

Choose the correct answer to complete the sentence. "With clear evidence, his company couldn't deny having _____ a large quantity of toxins into the sea."

A computer networks usually includes either selected employees of a particular business or or people who do not work together but have similar interests.

Chicago’s Sears Tower, now the tallest building in the world, rises 1,522 feet from the ground to the top of it antenna.

Oil spills are having a devastating effect on coral reefs in the ocean.

The native people of the Americans are called Indians because when Columbus landed in the Bahamas in 1492 , he thought that he has reached the East Indies.