A:or else
B:or rather
C:rather tha
D:more tha
He turned from side to side, eyeing himself in the mirror with a serious, studied ______ that soon changed into a smile.
观察下图,请将下列地区的英文字母代号填入答题卡(卷)图中对应的方框内。
A.丝绸之路上的重要地区:河西走廊
B.丝绸之路上的重要地区:葱岭
X
﹣1
0
1
2
P
a
b
c
112
若E(X)=0,D(X)=1,则a,b的值分别为( )
人体产生卵细胞、形成受精卵及胚胎发育的场所分别是( )