价格下降幅度最大的商品是（）。

A．大宅门

B．中国问题报告

C．罗大佑经典

D．三角洲部队

It was she that _____ a sharp whistle, which makes ______ possible for us to catch the thief. [ ]

A. gave off; this

B. gave out ; that

C. gave ; it

D. sent out ; them