企业建立电子商务网站通常有两个目的：其一是信息发布及塑造企业形象，其二是从事（）。
参考答案：商务活动
I would have come earlier，but I________that you were waiting for me.[ ]
A．hadn’t known
B．didn’t know
C．would have known
D．haven’t known
能携带氨基酸到蛋白质合成场所的核酸是（）
A.tRNA
B.mRNA
C.rRNA
D.hnRNA
E.DNA
