Most animals on land are known to us，but many living things underwater are not．Now let's get to know some of them．

Sea cucumber

Sea cucumbers are strange animals living at the bottom of the sea．They wear brown or pale green coats with many sticks up．When summer comes，they stay deep to sleep because they are afraid of heat．And when it is autumn，they move to shallow （浅的） water and get their food．

Pike

The pike is a kind of freshwater fish．They are good swimmers and like swimming near boats，waiting to be fed．They have sharp teeth to catch fishes．When they are young，they live in groups．However，when they grow up，they prefer to live alone．

Cuttlefish

A cuttlefish can swim quite fast，so it is also called rocket（火箭） fish．It has eight arms and two feelers on its head，just around its mouth．It ejects ink （喷墨） when it is in danger．Its meat is delicious，and it is often the first choice for many people．

Octopus

An octopus has long arms，with which to catch food and protect itself．When it is sleeping，one or two of its arms are still on duty，keeping moving．Once it feels something dangerous，it can wake up at once to take action．

49．Sea cucumbers stay deep to sleep in summer because they 　 　．

A．	are afraid of high temperature
B．	want to get strong and fat
C．	are afraid of their enemy
D．	want to live alone

50．According to the passage， 　 　likes to swim near boats．

A．	the sea cucumber
B．	the pike
C．	the cuttlefish
D．	the octopus

51．What happens if a cuttlefish meets its enemy？ 　 　

A．	It rushes at the enemy at once．
B．	It cuts off one of its arms．
C．	It bites with its sharp teeth．
D．	It ejects ink to the enemy．

52．The 　 　of an octopus can help protect it when in danger．

A．	color
B．	arms
C．	sound
D．	smells．