下列活动可以改变非洲国家“单一商品经济”的是

A．出口可可

B．出口咖啡

C．出口菠萝

D．发展农产品加工业

—Why was the headmaster in our school very pleased?

—Because the students in our school ________a Green City Project last year.[ ]

A. set out              

B. set off

C. set up                

D. send up