以下哪项不是河北省海水的主要污染物?()
A.无机氮
B.汞
C.化学需氧量
D.活性磷酸盐
参考答案:B
集艺术家、教育家于一身的戏曲大师,被誉为京剧鼻祖的是___________。
On his way home yesterday , Tom was hit on the head_____he had time to realize what was happening .
A.since
B.before
C.when
D.until