题目

父本基因型为AABb，母本基因型为AaBb，其F1不可能出现的基因型是：      A．AABb           B．Aabb           C．AaBb           D．aabb 答案：DWe were reading the newspaper            suddenly the light went out. [     ]A. when                   B. whileC. as soon as               D. before