单项选择题
The main advantage of improved Simplex tailshaft seal are（）
A.the good sealing performance and the simple structure B.the good sealing performance and the short life expectancy C.the good sealing performance but the short life expectancy D.the good sealing performance and the lower cost
单项选择题 Simplex tailshaft seal equipment’s working condition is terribleThe main cause is （）
单项选择题 The center line condition of the transmission shaft can be checked by（）
单项选择题 In the navigation（） cause the shafting over load easily.
