问题补充:
单选题ItisthoughtthatonebillionpeopleItheworld,_____ishalftheword’sworkers,earntheirlivingbyfarming.A.ifB.thatC.whichD.what
答案:
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。