发生在原始胚盘形成后即受精后第13天以上()
A.双卵双胎
B.单卵双胎,双羊膜囊,双绒毛膜
C.单羊膜囊双胎妊娠
D.联体儿
E.单卵双胎,双羊膜囊,单绒毛膜
参考答案:D
下列物质中,属于纯净物的是 ( )
A.生理盐水
B.啤酒
C.食醋
D.蒸馏水
What do people usually eat at Easter?[ ]
A. Rice dumplings.
B. Mooncakes.
C. Candies and apples.
D. Chocolate eggs.