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1/

2. Because of the polluted water, we can't swim in that river. 

3. Because of having sore leg, Nga had difficulty in walking. 

4. Because he behaved badly, he found himself in trouble. 

5. Because the weather was cold, we didn't go out for a walk. 

2/

1. Good

2. Happy 

3. Carefully 

4. Careful 

3/

2. He is a quick swimmer.

3. They play soccer skilfully. 

4. Mai is good at English. 

4/

2. Aren't / will drop 

3. Study / will pass 

5/

2. If you are careful, you will fall over the rocks. 

3. If Ha works harder, she will pass the exam. 

4. If you don't hurry up, you can't catch the bus. 

5. If you eat more vegetables, you will feel healthy.