-What’s the chance of there _____an election this year?

- I have no idea.

A．is

B．to be

C．being

D．be

乳糖操纵子中I基因编码产物是

A．乙酰基转移酶
B．透酶
C．β半乳糖苷酶
D．一种阻遏蛋白
E．一种激活蛋白