Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.

          Water is our life source. It makes up 70% of our bodies, and the average person actually spends about six months of his life on the bath or a shower. But we are only now learning  how to take care (1)______ water. Acid rain has polluted as many as 18,000 lakes. Our seas and rivers are (2)______, too. It is now very expensive to overcome the damage that has been done. (3)______, we have some hope for the future  because  some new sources of water have been discovered. People(4) _____live in Sahara have found fish swimming in deep underground streams. Many scientists also believe that there is a huge lake underneath London. If we have leant something from our (5)______, we should keep these new sources of water clean.

But we are only now learning  how to take care (1)______ water.