玉米叶肉细胞中的核酸，含有的碱基和核苷酸的种类分别是 [ ]
A．1种、2种
B．8种、8种
C．4种、4种
D．5种、8种
答案：D
6.They planted some young trees in the garden _______ it was the best time for them.
A．where
B．that
C．until
D．when
简述亲属身份行为的基本特点？
