题目:
I walked slowly through the market, where people__________all kinds of fruits and vegetables.
I studied the prices carefully and bought what I needed.
A.sell
B.were selling
C.had sold
D.have sold
答案:
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题目分析:本题有两种作法:第一种作法:根据反射光线反向延长过像点,作出反光点的像点S′,再根据平面镜成像的特点:像与物关于平面镜对称作出发光点S的位置,补出入射光线.第二种作法:根据光的反射定律:反...