我国已颁布的产品认证标志的类别有（）。
A.PRC标志
B.SC标志
C.方圆标志及其变形
D.萌芽标志
E.长城标志
参考答案：A, C, E
句型转换。
1. We can wear hats in school. (变成否定句)
_____________________________
2. We can eat in the cafeteria. We can't eat in the classroom. (用but 将两句话连接起来)
_____________________________
3. You have to wear sneakers for gym class. (变成一般疑问句,并作肯定回答)
4. I have to do my homework after school. (就划线部分提问)
5. I have to be in bed by ten o'clock. (就划线部分提问)
调查研究的基本抽样方法有几种（）
A.1
B.2
C.3
D.4
E.5
but 将两句话连接起来)