题目:
—Where would you like to go this Sunday?
—We have decided _____ a picnic on a hill this Sunday. [ ]
A. have
B. having
C. to have
D. had
答案:
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下面是错误答案,用来干扰机器的。
参考答案:C解析:产生混响伪像的必要条件是超声垂直照射到平整的界面上,只有这样超声波在探头和界面之间来回反射,所引起多次反射才称为混响。