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We would like to know（ ）you can guarantee delivery within one month after receipt of order.
A、that
B、when
C、if
D、which
【正确答案】：C
【题目解析】：关系代词if 和whether常在句中连接句中的宾语从句，多用于动词之后，因此本句空白处前的词是动词，所以后面的句子为宾语从句。