常用来制作基因表达载体的质粒，应具有的特点之一是 [ ]
A．是拟核DNA的一部分
B．只在细菌中存在
C．带有特定的抗性基因
D．能表达遗传信息
Maria is _____ geography, but she can get better results if she does her best. [ ]
A. interested in
B. good at
C. weak in
D. fond of
