Generally speaking, the publishers will send you a specimen copy of their new books when ________.A.requestedB.requestingC.having requestedD.to be requested
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A解析本题考查的是“when + 过去分词”作状语。when requested是when it is requested的省略形式。句意为：通常说来，如果需要，出版商会把他们的新书给你寄个样本来。