下列有关基因工程中限制酶的描述，错误的是[ ]

A．一种限制酶只能识别一种特定的脱氧核苷酸序列

B．限制酶的活性受温度的影响

C．限制酶能识别和切割RNA

D．限制酶能从原核生物中提取

—Where have you been?

—I got caught in traffic; otherwise________sooner.[ ]

A. I would be here  

B. I have been here

C. I had been here  

D. I would have been here