在有火源的情况下，氢气94.3%和氧气5.7%的混合物有爆炸危险。
参考答案：对
After studying in a medical college for five years, John _______ her job as a doctor in the countryside.
A．set out
B．took up
C．set up
D．set off
《中国居民膳食指南》推荐每人每天的油脂摄入量为多少克？（）
A.25
B.50
C.75
D.100
