核酸中核苷酸之间的连接方式是
A．2'，3'-磷酸二酯键
B．3'，5'-磷酸二酯键
C．2'，5'-磷酸二酯键
D．糖苷键
E．肽键
参考答案：B
Li Ning was able to set up a school for gymnasts in 1991, ______ he has continued to help young people to achieve their sporting ambitions.
A．when
B．dring which
C．since then
D．since when
我国外交政策的宗旨是
A．维护我国的独立和主权，反对霸权主义 B．维护世界和平，促进共同发展 C．争取较长期时期的和平国际环境 D．争取较长时期的良好周边环境
