问题
单项选择题
The product was processed ( ) official veterinary supervision.
A. in
B. under
C. after
D. with
答案
参考答案：B
搜题请搜索小程序“爱下问搜题”
The product was processed ( ) official veterinary supervision.
A. in
B. under
C. after
D. with
参考答案：B
，电子质量为
，电量为
，求电子绕核运动的周期。（静电力常量为
）