We do not know if sharks migrate from one region to another, but it has been established that the majority swim unceasingly, day and night. There are two reasons for this. Sharks do not have a swimming bladder . If sharks stop swimming they will sink. Also, most species have no mechanism for pumping water so that it will pass over their gills and bring oxygen into the bloodstream. They must depend on constant movement for this breathing.

　　26. According to the writer, if we see a shark approaching, we should_______.

　　A. cry out in water B. ring a bell

　　C. beat the water with our hands D. keep silent

　　27. Which of the following adjectives can best describe the sharks rush towards the spot where some blood is?

　　A. Criminal. B. Senseless.

　　C. Helpless. D. Terrified.

　　28. In Paragraph 3, the writer describes the behavior of sharks in order to show_______.

　　A. the influence of its behavior B. the adaptation of its behavior

　　C. the unpredictability of its behavior D. its difference from dog or crow

　　29. Which of the following statements about sharks is TRUE?

　　A. They are various kinds of puppets.

　　B. Most of them swim from one place to another every year.

　　C. Most of them keep on swimming without stopping.

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