The boy did his homework with the help of his father in the past. But now he can do it alone.

A．for himself

B．on himself

C．by himself

D．with himself

O/W型乳剂基质或水性凝胶基质中的防腐剂（）.

A．羟苯乙酯 

B．单硬脂酸甘油酯 

C．十二烷基硫酸钠 

D．甘油 

E．平平加