抹香鲸头部巨大，下颌较小，仅下颌有牙齿。主要食乌贼。体长可达（)米，体重超过50吨，是体型最大的齿鲸，头部可占身体的1/3，无背鳍;潜水能力极强，是潜水最深，潜水时间最长的哺乳动物。

共用题干
The Greatest Mystery of Whales
The whale is a warm-blooded,air-breathing animal,giving birth to its young alive,sucking them-and, like all mammals,originated on land.There are many______(51)of this.Its front flippers（鳍状肢）, used for steering and stability,are traces of feet.
Immense strength is______(52)into the great body of the big whales,and in fact most of a whale's body is one gigantic muscle.The blue whale's pulling strength has been estimated______(53) 400 horsepower.One specimen was reported to have towed（拖）a whaling vessel for seven hours at the ______(54)of eight knot（节）.
An angry whale will______(55).A famous example of this was the fate of Whaler Essex, ______(56)was sunk off the coast of South America early in the last century.More recently,steel ships have______( 57 ) their plates buckled（使弯曲）in the same way.Sperm whales（抹香鲸）were known to seize the old-time whaleboats in their jaws and crush them.
The greatest______(58)of whales is their diving ability.The sperm whale dives to the bottom for his______( 59 ) food , the octopus（章鱼）.In that search he is known to go as far down as 3 , 200 feet, where the______(60)is 1,400 pounds to a square inch.Doing so he will______(61) underwater as long as one hour.Two special skills are involved in this storing up enough______(62) (all whales are air-breathed)and tolerating thern great change in pressure.Just how he does it scientists have not______(63).It is believed that some of the oxygen is stored in a special ______(64)of blood vessels,rather than just held in the lungs.And it is believed that a special kind of oi1 in his head is some sort of a compensating mechanism that______(65)adjusts the internal pressure of his body.But since you can't bring a live whale into the laboratory for study,no one knows just how these things work.
61._________
A:set
B:become
C:remain
D:rest