声波在砼中的传播速度是分析桩身质量的指标之一，一般其完好桩的声速应为（）

Cats are creatures of habit.They like to go to sleep ab...

单项选择题Cats are creatures of habit.They like to go to sleep about the same time every day and for a certain length of time.They seem to have a natural clock inside them that tells them when to sleep.
Cats increase their regular sleep with occasional cat naps（打盹）.Some experts feel that humans could also benefit from this habit.Cat naps help to build up energy in the body.They are also a good way to get rid of trouble!Since cats have the same moods（情绪）as humans,some experts behave that people can improve their moods.People might become happier.
A number of famous people have copied cats by taking cat naps during the day.The naps would usually last from 15 to 30 minutes.
Winston Churchill took cat naps.So did Presidents Harry Truman,John F.Kennedy and Lyndon B.Johnson.These famous men were known for their energy.They were also able to work long hours,often into the night.Napping was their secret.
Perhaps more people learn from cats and take naps to feel better and live longer!
This selection was probably written to__________.

中国海洋生态系统存在的问题？ A. 过度捕捞 ...

多项选择题中国海洋生态系统存在的问题？ A.
过度捕捞 B.
海洋环境污染 C.
海洋生境破坏 D.
过度的水产养殖 E.
海岸侵蚀

Cats are creatures of habit.They like to go to sleep ab...

单项选择题Cats are creatures of habit.They like to go to sleep about the same time every day and for a certain length of time.They seem to have a natural clock inside them that tells them when to sleep.
Cats increase their regular sleep with occasional cat naps（打盹）.Some experts feel that humans could also benefit from this habit.Cat naps help to build up energy in the body.They are also a good way to get rid of trouble!Since cats have the same moods（情绪）as humans,some experts behave that people can improve their moods.People might become happier.
A number of famous people have copied cats by taking cat naps during the day.The naps would usually last from 15 to 30 minutes.
Winston Churchill took cat naps.So did Presidents Harry Truman,John F.Kennedy and Lyndon B.Johnson.These famous men were known for their energy.They were also able to work long hours,often into the night.Napping was their secret.
Perhaps more people learn from cats and take naps to feel better and live longer!
Naps usually last__________.