题目

— Could you tell me _______? I must find him.       — Sorry. I don’t know. But he was here just now.       A. where Tom was          B. where has Tom gone       C. where Tom is            D. where can I find Tom 答案：C下列有关生物工程的叙述中，不正确的是A.胚胎工程可提高优良种畜繁殖效率，基因工程可定向改变生物性状B.PCR的操作流程是：先高温变性、然后中温延伸、再低温复性C.生态工程主要是对不良的生态系统进行修复、改良或重建D.利用基因工程和植物体细胞杂交技术都可克服生殖隔离的限制