【单选题】This story was very exciting.I ___ it before.
【简答题】7 A. I stopped taking violin lessons, I never practiced. B. I stopped taking violin lessons because I never practiced. C. I stopped taking violin lessons. I never practiced.
【简答题】在三种RNA中,( )含量最多,( )含有的稀有碱基最多,( )半寿期最短。
【简答题】在生物细胞中主要有三种RNA,其中含量最多的是 ,种类最多的是 ,含有稀有碱基最多的是 。