在统计时段内，高于、低于年平均水位的机会相等的水位称（）。
A、高（洪）水位
B、中水位
C、低（枯）水位
D、平均水位
参考答案：B
用所给单词的适当形式填空。
1. Let's _____________ (put) the letter in the envelope.
2. Danny is _____________ (write) a letter to his friends.
3. She _____________ (want) to go shopping this afternoon.
4. They _____________ (have) fun yesterday.
5. You can _____________ (take) a picture with my camera.
How much for one melon?[ ]
A. It's 5 yuan.
B. It's expensive.
C. It's 5.
