[单选题]
For a wave traveling
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s t;4d8 gd3kg p kkrr:8-j6l6yecway9 of the particles' displacement with distance travelled is shown in the following graphs, which represent the wave at different moments in time of a wave travelling to the right.
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Graph I shows the wave at t=0s, while graph II is at t=1s.
The time difference between the two graphs is less than the wave's period.
Graph I
Graph II
What is the wave speed?