问题
单项选择题
While the total number of farmers engaged in agricultural production is barely half ______ it used to be in 1959, the size of the average farm has tripled.
A．that
B．what
C．which
D．how
答案
参考答案：B
解析：half what it used to be相当于half the number that it used to be, what既代替先行词the number又引导一个从句，其他几个选择项均没有这个功能。