Creatures in the sea were thought to live completely indepen

Creatures in the sea were thought to live completely independent of fresh water by certain type of adaptation (适应),but now researchers have discovered that one species,the yellow-bellied sea snake,in fact relies on rain for drinking water,and in between the rains is able to make do in an extreme state of dehydration (脱水).
Several studies have shown a link between fresh water availability and the places where yellow-bellied sea snakes live.The only source of freshwater in the sea is rainfall.During rainy periods,rainwater floats at the top of the seawater and provides a drink for those thirsty yellow-bellied sea snakes.Since sea snake populations often gather around those places where there are heavy rainfalls,researchers believed they depend on the water for survival.
If this is true,it must mean the yellow-bellied sea snake can survive extreme dehydration.To see if this is indeed the case,researchers caught 500 yellow-bellied sea snakes on the coast of Costa Rica.
They found that the snakes tended to drink more water following periods of low rainfall,and the lighter they were (and thus the more dehydrated they were),the more they drank.Their findings show that the yellow-bellied sea snake can live in a dehydrated state for several months at a time,depending on the length of the dry season.
The study proves that animals that once lived on land but then moved into the sea have developed a unique way of adaptation to their salty home.For instance,whales and sea turtles no longer need any freshwater at all by having salt glands (盐腺) that deal with seawater.Instead of adapting to the sea environment like many others,sea snakes have taken a different approach.
47.According to the text,people used to think that 　　　.
A.sea snakes can go without fresh water
B.sea snakes can take salt out of their bodies
C.sea snakes adapt to saltwater in a special way
D.sea snakes can turn saltwater into fresh water
48.The underlined phrase “make do” in the first paragraph probably means “　　　 ”.
A.stay up late　 B.manage to live　　 C.live an easy life　 　D.pretend to be dead
49.What did the research on the 500 yellow-bellied sea snakes prove?
A.They seldom drink except when it is raining.
B.They become lighter after drinking fresh water.
C.They can live in a dehydrated state for a long time.
D.They refused to drink after being caught.
50.What is the best title for the text?
A.What sea snakes drink for living
B.How sea snakes survive without water to drink
C.How sea snakes differ from other sea animals
D.Why sea snakes move from land to the sea