预防上呼吸道感染的关键是___________________。
参考答案：增强机体抵抗力
The PPC was founded on __________. Thanks to our Party, we're living a happy life.[ ]
A. July 1st, 1921
B. August 1st, 1928
C. October 1st, 1949
D. May 4th, 1919
制备空胶囊时加入丙二醇的作用是
A．遮光剂B．溶剂C．成型剂D．增塑剂E．增稠剂
