问题
选择题
The accident ______ the other day.[ ]
A. happens
B. has happened
C. does happen
D did happen
答案
答案：D
搜题请搜索小程序“爱下问搜题”
The accident ______ the other day.[ ]
A. happens
B. has happened
C. does happen
D did happen
答案：D
），试求其频谱F（ω）。