(1)____________________________________________________.But there are advantages to living in water.The cold and dark water played an important role in making fish what they are.One is that water doesn't change much to the sudden temperature changes in the air.Therefore it makes an excellent living place for a cold blooded animal.Another advantage is the water's ability to easily support body weight.A fish in water is almost weightless. (2)__________________________________________.One, a fish can get along with a light weight and a simple bone structure.Because of water's floatation, whatever the size of the fish, it can swim very freely.Yet there is one basic difficulty to living in water the fact that it can't be pressed.For a fish to move through water, it must actually push the water aside.Most can do this by wiggling back and forth in snakelike motion.The fish pushes water aside by the forward motion of its head and with a curve of its body and its tail moving to right and left.Water helped to shape the development of fish.(3)________________________________________.And for this reason, fish have a basic shape that is beautifully adapted to deal with the fact that it can swim freely in the water without difficulties.
