若一个锐角∠α=37°47′，则∠α的余角为______．
∠α的余角=90°-37°47′=52°13′．
故答案为：52°13′．
—Is your father in?
—No, he _____ for three hours.[ ]
A. was out
B. has been out
C. went out
D. has gone out
下列哪一项不属于上颌窦穿刺术的并发症（）
A.气栓形成
B.眶内血肿
C.脑脊液鼻漏
D.晕厥
E.鼻黏膜撕裂
