常喝牛奶可有效防治骨质疏松症,原因是其含有丰富的( )
A:钙
B:碘
C:糖类
D:膳食纤维
如图,AB⊥BC,AD⊥DC,∠BAD=120°,在BC、CD上分别找一点M、N,当△AMN周长最小时,∠AMN+∠ANM的度数是____.
—_____ He didn't even spend a single hour preparing for it.