有的人头发表面经常出现白色头皮屑,这是头皮皮脂腺分泌和表皮角质层的新陈代谢作用而产生的,属()。
A.正常现象
B.病理现象
C.一般现象
D.异常现象
参考答案:A
Wu Bin, a bus driver, saved 24 passengers on the large bus after he _______ by a piece of metal while he was driving.
A. is hit B. was hit
C. has hit D has been hit
关系数据库的关系演算语言是以 【5】 为基础的DML语言。