题目

He's more of a talker than a doer, which is _____ he achieves nothing. A . why B . when C . where D . that 答案：A某DNA片段所转录的mRNA中尿嘧啶占28%，腺嘌呤占18%，则这个DNA片段中胸腺嘧啶和鸟嘌呤分别占 A．46%、54%        B．23%、27%         C．27%、23%        D．46%、27%