It is thought that one billion people in the world is half the world’s workers earn thei

问题补充：

It is thought that one billion people in the world, is half the world’s workers, earn their living by farming.

A. if

B. that

C. which

D. what

答案：

A. if

(答案→)B. that

C. which

D. what

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

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