下列物质中属于纯净物的是（）

$-\frac{1}{2}$的倒数是（    ）

    Tomorrow is Children's Day. Xiaofeng is very happy. In the morning, he is going to the shopping mall with his mother. He is going to buy a new shirt. In the afternoon, he is going to the park. He is going to play ping-pong with his friends. In the evening, he is going to the movie theater. He's going to see a movie.