It is thought that one billion people I the world, _____is half the word’s workers, earn their living by farming.
A.if
B.that
C.which
D.what
网友回答
B解析句中“half the world’s workers”是对“one billion people in the world” 的补充说明， “that is”是 “that is to say”的省略说法，是插入语，that 并不是引导非限制性定语从句的，如果在 “that is”后加个逗号则更清楚，应选B。