题目

小清在显微镜下观察到了人的口腔上皮细胞后，兴奋地把显微镜轻轻挪动给同组同学看，但其他同学却看不清楚物像．要想重新看清物像，应首先考虑进行的操作是(     ) A．转动转换器   B．调节反光镜的角度 C．调节粗准焦螺旋   D．调节细准焦螺旋 答案：B There are so many kinds of pens in the shop ,I can't decide ________． [　　] A． when to buy B． where to buy C． what to buy D． which to buy