一列简谐横波由P点向Q点沿直线传播,P、Q两点相距1m。甲、乙分别为P、Q两质点的振动图象,如图所示,如果波长1m,则波的传播速度为多少?
解:T=0.8s,λ=4m
=5m/s
The train arrived Nanjing 6:00 _____ the afternoon of September.13. [ ]
A. at, at, in
B. in, at, in
C. in, at, on
D. at, in, on
对于暂存公文的保管,密件与非密件不必分开。