气相色谱仪中电子捕获检测器要求用氮气作载气，氮气纯度至少应为（）

A.99.00%

B.99.95%

C.99.98%

D.99.90%

E.99.99%

The most accurate method of determining gyrocompass error while underway is by（）.

A.Comparing the gyro azimuth of a celestial body with the computed azimuth of the body

B.Comparing the gyro heading with the magnetic compass heading

C.Determining from the chart the course made good between celestial fixes

D.It cannot be determined accurately at sea due to drift of unknown currents