单选题 Many institutions of higher education suffer declining enrollments during periods of economic slowdown. At two-year community colleges, however, enrollment figures boom during these periods when many people have less money and there is more competition for jobs.
Each of the following, if true, helps to explain the enrollment increases in two-year community colleges described above EXCEPT:

A、 During periods of economic slowdown, two-year community colleges are more likely than four-year colleges to prepare their students for the jobs that are still available.
B、 During periods of economic prosperity, graduates of two-year community colleges often continue their studies at four-year colleges.
C、 Tuition at most two-year community colleges is a fraction of that at four-year colleges.
D、 Two-year community colleges devote more resources than do other colleges to attracting those students especially affected by economic slowdowns.
E、 (E) Students at two-year community colleges, but not those at most four-year colleges, can control the cost of their studies by choosing the number of courses they take each term.

【正确答案】 B

【答案解析】[解析] 四个选项就在经济增长放慢时期为什么许多人选择上两年制大学这个问题，提出了理由。选项(A)指出当经济状况不景气时，两年制的大学教育可以提供一个找到工作的更好机会；选项(C)和(E)指出为什么收入减少的人们更愿意上两年制大学；最后，选项(D)指出两年制大学比四年制大学花了更多精力来吸引那些生活受到经济增长放慢影响的人。选项(B)是正确答案，可能解释了经济增长放慢时期四年制大学招收学生人数为什么下降，但因为它仅与两年制大学的毕业生有关，它不能解释为什么这些大学招收学生的人数会增加，另外，(B)为段落推理的否命题，而否命题与原命题不等价。