早晨7时应用效果最好的是
A．氨茶碱
B．沙丁胺醇
C．二羟丙茶碱
D．比沙可啶
E．钙尔奇D
参考答案：A
It is difficult for us to learn a lesson in life_________we’ve actually had that lesson.
A．until
B．after
C．since
D．when
我国安全生产的方针是（）
