阅读下面的日记，按要求完成任务。

April 12th

Dear Diary,

    Today was Sunday. In the morning I was going to have a picnic with my friends. But it was rainy. So I had to stay at home. I washed my clothes and cleaned the floor. After finishing the work, I was very tired.

    At three o'clock in the afternoon, my cousin Sarah asked me to see a film. I was happy. But I didn't find my pet kitten. Sarah and I looked for him here and there. Guess! Where was he? He was in my cap! When we came to the cinema, it was about four thirty. What a bad day!

Mary

判断（1）~（3）的正误，回答（4）、（5）的问题：

下列各近似数精确到万位的是（   ）

已知| $\overrightarrow{a}$ |=2，| $\overrightarrow{b}$ |=4，且 $\overrightarrow{b}$ 和 $\overrightarrow{a}$ 反向，用向量 $\overrightarrow{a}$ 表示向量 $\overrightarrow{b}$ =____．