________ his job application carefully, he emailed it to the company where he wanted to work.

A．Having checked

B．Checked

C．Checking

D．To have checked

大家对“兰亭”系列美白嫩肤护肤品熟悉后，大量女士顾客开始购买，市场逐步扩大。这是产品生命周期的（）

A．介绍期 

B．成长期 

C．成熟期 

D．衰退期