The number of college students in China_ gre atly since 1990A has increased B have increased C are increased D was increased
问题描述：
The number of college students in China_ gre atly since 1990
A has increased B have increased C are increased D was increased
答
选A
在"the number of college students in China"中，"the number"是修饰"college students in China"的，所以主语是”the number" ，是单数，所以动词应该用第三人称单数；
"since"表示从什么时候以来，对现在有影响，是一个非常明确的完成时状语，所以要用完成时。
答
这里就要弄清楚句子的成分与结构了，第一个have是做定语从句来修饰students的The number of the college students 能用单数吗? the college students
答
A
这句话的主语是number
since是一个非常明确的时间状语 有since 必然接完成时