As his friends, we have made up our minds to do everything we can ___him get out of trouble.   

A．to help

B．help

C．helping

D．Helped

能有效改善聚甲醛的加工流动性的方法有（）

A.增大分子量

B.升高加工温度

C.提高挤出机的螺杆转速