Ⅳ阅读理解（每小题2分，共40分）阅读下面短文，从所给的四个选项中，选出最佳答案。
We shall not drown（淹死）if we remember these rules:
1, Never swim alone.
2, Never swim at a beach if there is no lifeguard（救生员）.
3, Never swim after a meal or when you feel hungry or tired.
4, Never depend on rings, floats（漂浮物）or other swimming aids（助游具）. You may lose them or they may let you sink（下沉）.
5, Don’t stay in the water too long , especially if it is cold.
6, Before you dive, be sure the water is deep enough and you will not hit anybody.
7, Never go out in a boat if you can not swim or if you are not wearing a life jacket.
If you get into difficulty, this is what you should do :
1, Keep calm（镇定）. Save you strength and your breath.
2, Try to float on your back or tread（踩水）water. To tread water, move your feet as if you are climbing some stairs.
3, Raise your right arm for help.
Remember : a red flag means that it is dangerous for all swimmers to enter the water. A blue flag means that it is dangerous for children and weak swimmers to enter the water.
1. When you see a red flag, you know that ______ swim there.
A. no one should                     B. anyone may    
C. only strong swimming should         D. children should not
2. We can go swimming ________.
A. after a meal                      B. if we have a ring  
C. when the water is dirty             D. when we are not alone
3. We should dive only when _______.
A. the water is deep enough           B. the water is cold
C. the water is warm                 D. we are not alone
4. What the writer wants to say is that ______.
A. rings and floats are of no use           B. boats are not safe
C. we must be very careful in swimming    D. swimming is bad for your health