管道共振
参考答案：管道的固有频率或气柱固有频率与激发频率相同时发生的振动。
I am extremely _____ at the way he always stares at me in the office. [ ]
A. trouble
B. worried
C. annoyed
D. anxious
We have been told that under no circumstances_______ the office telephone for personal affairs.
A．may we use
B．we can use
C．we could use
D．did we use
