A:f'x>0,g'x>0
B:f'x>0,g'x<0
C:f'x<0,g'x>0
D:f'x<0,g'x<0
化学兴趣小组欲探究自己使用的某品牌牙膏的主要成分。
在有石块的河里游泳的人上岸时,由深水走向浅水的过程中,以下体验和分析合理的是( )
J____ from his face on which there was a confident smile, we know that he didn't lose heart.