有的幼儿吃了很多钙片,但仍患佝偻病,主要原因是缺乏( )
A:维生素D
B:维生素A
C:维生素B
D:蛋白质
计算下面图形的周长及面积。
“One tree can't make a forest” tells us no one would be heroes ____ (with) his friends.
下列算式中错误的是( )