单项选择题 A．鸟苷酸 B．尿苷酸 C．腺苷酸 D．胸苷酸真核生物mRNA帽子结构中被甲基化的核苷酸是A． B． C． D．

单项选择题 听力原文：M: How about seeing a film this evening?W: When?M: It begins at 7: 15. We'd better get there at 6:50.W: Oh, sorry. My mother will leave for London this evening. I'm seeing her off at 7: 00.When will the woman's mother leave for London?A．7:15B．7:00C．6:50

单项选择题 听力原文：How often does your group meet?(A) Okay, I'll see you at the meeting.(B) Once a month.(C) Upstairs at 3 o'clock.(1)A． B． C．