根据句意及首字母提示，补全单词。

1. Do you know the whales are the e_      __ animals in the sea?

2. The little monkey is very p______.  Look! He is trying to catch the food from his mother.

3. More and more rivers are p__       _ by the chemical factories.  Our drinking water is less and less.

4. All of teenagers will get best e    ____ in our village with the help of our teachers.

5. Can you w_           how heavy the elephant is without any help?