以1949年为基期，2000年为报告期，计算产品产值的平均发展速度应开（）次方。
A.49
B.50
C.51
D.52
参考答案：C
选择in, on, of, to, for, from填空，完成对话。
1. A: May I speak ______________ Miss Green?
B: Sorry, she's not in.
2. A: Tom, this new shirt is ______________ you.
B: Thank you, Mum.
3. A: Excuse me, where's the classroom ______________ Class One?
B: Room 201.
4. A: Are you ______________ Beijing?
B: No, I'm not.
5. A: What's ______________ the letter box?
B: Many letters.
6. A: Are there any books ______________ the shelf?
B: Yes, there are.
何谓光电池的开路电压及短路电流？为什么作为检测元件时要采用短路电流输出形式？
