The summer beach season is prime time for shark attacks. It seems like sharks are attacking all the time. But that is something of an illusion. The number of attacks is very small.
How does a shark hunt? Muscles and fins give the shark its speed and maneuverability in the water. A shark’s front fins act like the wings of a plane and let it “fly” through the water. The tail acts like a high-power propeller
But the big thing that gives the shark its edge in the ocean is its sensory package. The package includes the shark’s eyes, ears, skin, nose and mouth, as weir as electric sensing.
A shark’s nose is probably its most important sense. If you were to put a single drop of blood in a swimming pool, a great white shark could smell that. And they can tell the direction that the smell is coming from.
Sharks handle their electric sensing using cell located in the head. Whenever something moves using its muscles, a shark can detect the electrical impulses flowing to those muscles. A shark can electrically “see” anything that has muscles even if it is hiding or the water is not clear.
Sharks even have vibration sensors in their skin. Even something moves near the shark, tubes pick up the pressure changes and hairs inside the tubes send signals to the brain. This extra sense allows a shark to turn quickly and attack again.
When you put all these different senses together , it makes the shark a nearly ideal hunter. A shark can detect prey from miles away and then use eyes, electrosensing and movement sensing to home in.
Strangely, sharks do not seem to use these senses to home in on people. The very low number of sharks tells us that sharks do not hunt people in a regular basis. On the other hand, people love to hunt sharks, Millions of sharks die every year.  Without protection, extinction is a definite possibility.
68.From the text, we can know that_________________.
A. it is true that sharks are attacking all the time
B. a shark can see anything that has muscles even if it is hiding.
C. sharks deal with their electric sensing using cell located in the skin
D. what gives the shark its speed and maneuverability is fins and muscles
69.What gives the shark its edge in the ocean according to the text?
A. Its muscle.                                               B. Its nose.                      
C. Its sensory package.                                     D. Its fins
70. The underlined phrase home in on means___________.
A. swim                B. move                  C. hunt                       D. smell
71.In this text, the writer implies that__________.
A.there ara many shark attacks                     B. humans beings should protect sharks    
C. human beings dislike hunting shark             D. sharks’ nose is very important