烤瓷冠桥烧结后,颜色呈“白垩”状,其最主要的原因是 ()
A.烧结后冷却过快
B.烧结后冷却过慢
C.真空度过低
D.真空度过高
E.烧结速度过快
参考答案:C
There __________ many people at the square.[ ]
A. is
B. are
C. be
血型及血液蛋白质型用途?