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
--- Excuse me, could you tell me how ______ to Beijing Zoo?
--- Well, you may take Bus No.27.
A．get
B．gets
C．getting
D．to get
5，3，2，1，1，( )
A．-3
B．-2
C．0
D．2
