—Sorry，I can't go camping with you. I have to prepare well enough

　for the entrance exam.

—________！We can camp together next time.

A．Don't say so

B．Congratulations

C．Good luck

D．No problem

用显微镜观察叶绿体和细胞质流动。请回答下列问题。

(1)为什么选用黑藻的幼嫩叶片而不是幼根为材料观察细胞质流动？_____________________。

(2)如果先用高倍镜观察，可能会出现什么情况？____________________。

(3)叶绿体的形态和分布随_______的强度和方向的改变而改变。