题目

—This is the first time I _________ my picture with my own hands. —It’s time that you _________ a picture for me. A. have taken; took       B. took; took C. took; will take       D. will take; have taken 答案：A在实验课上，同学们分别制作了“洋葱表皮细胞”和“人口腔上皮细胞”的临时装片，并用显微镜观察细胞。请据图回答：（1）为了避免产生气泡，步骤⑤的正确操作方法是_______________________________。（2）显微镜中A是目镜；要使物像看得更清晰，需调节的结构是_______(填字母)。（3）小西同学观察到的口腔上皮细胞与洋葱表皮细胞相比，没有细胞壁(只需写出一个结构名称)；细胞中被染色最深的结构是细胞核，它是_________中心。