一粒种子能长成参天大树的奥秘在于种子中存在（  ）

如图，在⊙O中，$\stackrel{\wedge }{AB}$=$\stackrel{\wedge }{AC}$，∠ACB=60°，求证：∠AOB=∠BOC=∠AOC．

为提高树木的成活率，园林工人常常给树木输液（主要成分是水和无机盐）．你认为输液管的枕头必须插入到树干的（    ）

露西和杰克在初三以来的6次大型综合考试中，平均成绩都一样，但露西成绩的方差为1.2，杰克成绩的方差为0.8，则下列对露西、杰克这6次大型综合考试成绩的描述，正确的是（　　）

阅读理解。

Oliver: Good afternoon, Mike.

Mike: Good afternoon, Oliver. What time is it now?

Oliver: It's five fifty. Why?

Mike: My mother is ill. My father isn't at home. I must go home and cook dinner.

Oliver: I'm sorry to hear that. Can you cook meals?

Mike: Sure. And I can wash clothes, too.

Oliver: You're helpful. I can't do that, but I can clean the room.

Mike: You are also helpful! I have to go. Goodbye!

Oliver: Bye.

根据对话内容，选择正确答案。