问题
选择题
— Your pen is very nice.
— _____.
[ ]
A. Thanks you
B. Thank
C. Thank you
D. No,it isn't'
答案
答案：C
搜题请搜索小程序“爱下问搜题”
— Your pen is very nice.
— _____.
[ ]
A. Thanks you
B. Thank
C. Thank you
D. No,it isn't'
答案：C
，周期为T。t=0时刻的波形如图1所示，a、b是波上的两个质点。图2是波上某一质点的振动图象。下列说法正确的是