商检标志分为()
A.卫生标志
B.安全标志
C.质量标志
D.环境标志
E.体系标志
参考答案:B, C
—Do you often go to school _____ bike?
—No, I often go there _____ foot. [ ]
A. by; by
B. by; in
C. on; on
D. by; on
主板上安装配件的扩展插槽主要有哪些?