被子植物成熟胚囊中有2个（）。
A.卵细胞
B.反足细胞
C.次生核
D.助细胞
参考答案：D
There are two rooms in the apartment, ________ serves as a kitchen.
A．the smaller of them
B．the smallest of which
C．the smaller of which
D．smallest of which
原核生物DNA的合成是单点开始，真核生物为多点开始。（）
