题目

When he looked up, he suddenly found himself        by a group of teenagers,        looked at him anxiously. A．to be surrounded; which                       B．surrounded; who C．be surrounded; who                             D．having been surrounded; which 答案：B胰岛B细胞合成胰岛素的过程中，不需要（    ） A．脱氧核苷酸       B．核糖核酸         C．核糖核苷酸       D．氨基酸