Certainly no creature in the sea is odderthan the common sea cucumber. All living creatures, especially human beings,have their peculiarities, but everything about the little sea cucumber seemsunusual. What else can be said about a bizarre animal that, among othereccentricities, eats mud, feeds almost continuously day and night but can livewithout eating for long periods, and can be poisonous but is consideredsupremely edible by gourmets？
For some fifty million years, despite allits eccentricities, the sea cucumber has subsisted on its diet of mud. It isadaptable enough to live attached to rocks by its tube feet, under rocks inshallow water, or on the surface of mud flats. Common in cool water on bothAtlantic and Pacific shores, it has the ability to suck up mud or sand anddigest whatever nutrients are present.
Sea cucumbers come in a variety of colors,ranging from black to reddish brown to sand color and nearly white. One formeven has vivid purple tentacles. Usually the creatures are cucumbershaped-hence their name-and because they are typically rock inhabitants, thisshape, combined with flexibility, enables them to squeeze into crevices wherethey are safe from predators and ocean currents.
Although they have voracious appetites,eating day and night, sea cucumbers have the capacity to become quiescent andlive at a low metabolic rate-feeding sparingly or not at all for long periods,so that the marine organisms that provide their food have a chance to multiply.If it were not for this faculty, they would devour all the food available in ashort time and would probably starve themselves out of existence.
But the most spectacular thing about thesea cucumber is the way it defends itself. Its major enemies are fish and crabs,when attacked; it squirts all its internal organs into water. It also casts offattached structures such as tentacles. The sea cucumber will eviscerate andregenerate itself if it is attacked or even touched; it will do the same if thesurrounding water temperature is too high or if the water becomes too polluted.
1. According to the passage， why is the shape of sea cucumbers important？
A. It helps them to digest their food.
B. It helps them to protect themselves from danger.
C. It makes it easier for them to move through the mud.
D. It makes them attractive to fish.
2. The fourth paragraph of the passage primarily discusses______.
A. the reproduction of sea cucumbers
B. the food sources of sea cucumbers
C. the eating habits of sea cucumbers
D. threats to sea cucumbers' existence
3. What can be inferred about the defence mechanisms of the sea cucumber？
A. They are very sensitive to surrounding stimuli.
B. They are almost useless.
C. They require group cooperation.
D. They are similar to those of most sea creatures.
4. Which of the following would NOT cause a sea cucumber to release its internal organs into the water？
A. A touch B. Food C. Unusually warm water D. Pollution.