The lake near our village is _______. It's dangerous to swim in it.
A:40 metres' deep
B:40-metre deep
C:40 metres deep
D:40-metres-deep
质粒是基因工程最常用的运载体,它的主要特点是①能自主复制 ②不能自主复制 ③结构很小 ④蛋白质 ⑤环状RNA⑥环状DNA ⑦能“友好”地“借居”