陈向东归纳9

9 Consider three fish swimming together in a school. The space within which each fish can be seen by predator Y is defined by a sphere centered on the fish and having a radius that is the maximum distance Y can see. The school is vulnerable to attack when Y is within one of the three spheres. The spheres overlap to a great extent, since the fish are in a compact group.

Which of the following is a reliable inference to be drawn from the passage above?

(A)         The vulnerability to attack of the school as a whole is not much greater than the vulnerability to attack of any one fish in the school.

(B)         There is less chance that predator Y will attack a school of four fish than that it will attack a school of three fish.

(C)         Fish who swim I schools are less likely to be devoured by predators than are fish who do not swim in schools.

(D)     The maximum distance at which an individual fish is visible depends less on the size of the fish than on whether the fish is swimming in a school.

(E)         The maximum distance at which predator Y can see its prey is increased if Y is itself swimming in a school of Y’s.

答案：A

虽然BCDE很明显不能从文中推出，但是A又是怎样依据前提和结论推出的。