读短文，选择正确答案。

      Zhang Yun is a teacher. She teaches music. She likes singing. She works in a primary school (小学).

She goes to school by bus.

1. — What does Zhang Yun do?

    — Zhang Yun is a ___________. 

A. teacher

B. nurse

C. salesperson

2. Zhang Yun likes ___________.

A. collecting stamps

B. singing

C. riding a bike

3. Where does Zhang Yun work? 

A. In a hospital.

B. In a supermarket.

C. In a school.

4. — How does Zhang Yun go to school?

    — Zhang Yun goes to school ___________.

A. by subway

B. by bike

C. by bus

如果在一个非零无符号二进制整数后添加一个0，则此数的值为原数的______。

A．1/4
B．1/2
C．2倍
D．4倍