单项选择题
All of the following are part of the fire triangle EXCEPT（）.
A.fuel B.electricity C.oxygen D.heat
单项选择题 All Loran-C transmitting stations are equipped with cesium frequency standards which permit （）.
单项选择题 Air circulation is caused or affected by（）.
单项选择题 Aids to navigation marking the intracoastal waterway can be identified by（）.
