Medical students have to follow a course lasting for ............

If you have a desire to travel, when does the writer suggest that you do it?

What is the most important purpose of the ozone layer?

What can be inferred about machines that are not calculators or computers?

As a result of pollution, Lake Erie, on the borders of the USA and Canada, is now without any living things. Pollutions in water are not simply a matter of “poisons” killing large numbers of fish overnight. Very often the effects of pollution are not noticed for many months or years because the first organisms to be affected are either plants or plankton. But these organisms are the food of fish and birds and other creatures. When this food disappears, the fish and birds die in this way a whole food chain can be wiped out, and it is not until dead fish and water birds are seen at the river’s edge or on the sea shore that people realize what is happening. Where do the substances which pollute the water come from? There are two main sources – sewage and industrial waste. As more detergent is used in the home, so more of it is finally put into our rivers, lakes and seas. Detergents harm water birds dissolving the natural substance which keep their feather waterproof. Sewage itself, if it is not properly treated, makes the water dirty and prevents all forms of life in rivers and the sea from receiving the oxygen they need. Industrial waste is even more harmful since there are many high poisonous things in it, such as copper and lead. So, if we want to stop this pollution, the answer is simple, sewage and industrial waste must be made clean before flowing into the water. It may already be too late to save some rivers and lakes, but others can still be saved if the correct action is taken at once. 

According to the passage, the way to stop water pollution is ...........

Pollution in water is noticed ............. 

The word “it” in paragraph 1 refers to ..............

According to the passage, all of the followings are TRUE except ___________.

The White House, the official home of the United States president, was not built in time for George Washington to live in it. It was begun in 1792 and was ready for its first inhabitants. President and Mrs.John Adams, who moved in on November 1, 1800. When the Adamses moved in, the White House was not yet complete, and the Adamses suffered many inconveniences; for example, the main staircase was incomplete, which hindered movement from floor to floor, and the future laundry yard was merely a pool of mud, so wet laundry was hung in the unfinished East Room to dry. Thomas Jefferson, the third president, improved the comfort of the White House in many respects and added new architectural features such as the terraces on the east and west ends. When the British forces burned the White House on August 24, 1814, President Madison was forced to leave.All the remained after the fire was the exterior walls, the interior was completely destroyed. It was not until December of 1817 that the following president, James Monroe, was able to move into a rebuilt residence. Since then, the White House has continued to be modified but has been continuously occupied by each succeeding U.S president. ing would be the most appropriate title for this text?

It can be inferred from paragraph 4 that__________.

Sixty years ago, most women ____________.