Blue whales are the largest animals in the world．But they are amazing（1） 　　because of their huge size， but their slow heartbeat．

For the first time， scientists have researched the（2） 　　of a blue whale．They found （3） 　　when blue whales dive（潜水） for food， their heart rates（心率） are as（4） 　　as 2 beats per （每） minute（bpm）．Scientists used to（5） 　　that their diving heart rate was 15 bpm．When the whales go to the ocean's（6） 　　to breathe， their heart rate is between 25 and 37 bpm．

Usually， the larger an animal is，（7） 　　its heart beats， since it takes more time to pump （输送） blood around（8） 　　body．Shrews， the smallest mammals（哺乳动物） ， have a heart rate of up to 1，000 bpm．Humans usually stay between 60 and 100 bpm．

（9） 　　slowing their heart rate， blue whales can send more blood to the muscles（肌肉） that they use（10） 　　．These muscles become stronger， allowing the whales to dive for longer periods of time．

（1）A．neither	B．either	C．not only	D．although
（2）A．heartbeat	B．body size	C．diving	D．food
（3）A．it	B．that	C．once	D．if
（4）A．many	B．little	C．fast	D．slow
（5）A．regard	B．expect	C．think	D．doubt
（6）A．bottom	B．surface	C．center	D．side
（7）A．the slower	B．slower	C．the faster	D．faster
（8）A．it's	B．its	C．his	D．her
（9）A．By	B．In	C．On	D．At
（10）A．to pump blood	B．to eat	C．to breathe	D．to dive