MHT CET Physics question

A horizontal plank has a rectangular block placed on it. The plank starts oscillating vertically and simple harmonically with an amplitude of 40 cm. The block just loses contact with the plank when the latter is momentary at rest, then

• (A)the period of oscillation is sCorrect
• (B)the block weighs double its weight when the plank is at one of the positions of momentary restCorrect
• (C)the block weighs 1.5 times its weight on the plank half way downCorrect
• (D)the block weighs its true weight on the plank when the latter moves fastestCorrect