题干
―Why are you so happy?
―Because the news _____ too exciting.
―Because the news _____ too exciting.
A：are
B：have
C：i
D：ha
答案(点此获取答案解析）
C
④共有8种核苷酸 ⑤共有5种核苷酸 ⑥A均代表同一种核苷