现有含CaO杂质的CaC2试样．某研究性学习小组的同学拟用以下三种方案测定CaC2试样的纯度（固体电石﹣﹣CaC2与水可快速反应生成难溶于水的C2H2，反应方程式为：CaC2+2H2O→Ca（OH）2+C2H2↑）．请填写下列空白：
读句子，按要求完成练习
啊，老桥，你如一位德高望重的老人，在这涧水上站了几百年了吧？
啊，老桥，你如一位老人，在这涧水上站了几百年了吧？
比较上面两个句子，哪个句子更好？为什么？
阅读下面材料,从每题所给的三个选项(A、 B和C)中,选出最佳选项,
Let's read the conversations and guess the meaning of the following expressions.
It's up to you.
A: What would you like for dinner tonight?
B: I'm not sure. What do you want?
A: It's up to you. Whatever you want, we will have.
In your dreams!
A: Guess what? This weekend, I caught a fish this big.
B: No way.
A: Yeah, it was huge!
B: In your dreams! It's impossible that you caught a fish that big.
Play it by ear.
A: Hey, what do you want to do this weekend?
B: I don't know. Maybe we can go to see a movie or have dinner. Why don't we play it by ear?
A: Sure. Let's decide as we go along.
Keep my fingers crossed.
A; Hey, How are you?
B: Hey, I am doing great. I did well in a job interview yesterday. I really hope to get the job.
A: Oh, have you heard back from them?
B: No, not yet. But I'm keeping my fingers crossed. Hopefully they'll ca11 me today.
Miss the point
A: Okay. So now do you understand?
B: I'm not sure. Can you explain it again? I think I missed the point.
A:. All right. I'll explain it one more time.
