种植玉米的施肥原则是什么？
参考答案：
以基肥为主，种肥、追肥为辅。基肥以有机肥为主；种肥以速效性P、K为主，配合少量微肥；追肥以N为主。
端末效应
The rated operating time of a self-contained breathing device may be reduced in actual use because of（）.
A.pressure differences in the atmosphere
B.the length of the hose attached to the facepiece
C.the physical exertion of the person wearing the device
D.spaces containing poisonous vapors
