问题
选择题
--- What's your cousin's age?
--- ______ . [ ]
A. He is 13 years old
B. She is fine today
C. She's 13 years
D. Sorry, I don't know
答案
答案：D
搜题请搜索小程序“爱下问搜题”
--- What's your cousin's age?
--- ______ . [ ]
A. He is 13 years old
B. She is fine today
C. She's 13 years
D. Sorry, I don't know
答案：D
开始振动时，速度方向沿
正方向
时，质点
通过的路程为