（）是企业产品发展的黄金阶段，营销策略的重点是突出一个“快”字。
A．成熟期
B．投入期
C．开发期
D．成长期
参考答案：D
— Just now Jenny gave ten dollars to a person in trouble.
— She _________ others. [ ]
A. was always helping
B. is always helping
C. always helped
D. had always helped
以下物质分子中不能以简单扩散方式透过细胞膜的是（）。
A.H2O
B.O2
C.尿素
D.葡萄糖
