许多人类学家认为,南方古猿是人类的始祖,他们生活在距今[ ]
A.约2100万年前
B.约3500万年前
C.约500万—100万年前
D.约1万—7千年前
答案:C
The ordinary girl sat silently at the corner, but when the prince came over to invite her to dance, her face immediately _________.
A.cheered up
B.lit up
C.turned up
D.made up
下列符号中,表示两个氢原子的是
A.H2
B.2H
C.2H+
D.2H2