76. A Gaussian wave packet travels through free space. Which of the following statements about the wave packet are correct for all such wave packets?
I. The average momentum of the wave packet is zero.
II. The width of the wave packet increases with time, as
.
III. The amplitude of the wave packet remains constant with time.
IV. The narrower the wave packet is in momentum space, the wider it is in coordinate space.
(A) I and III only
(B) II and IV only
(C) I, II and IV only
(D) II, III and IV only
(E) I, II, III and IV
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