The successful operation of any engine or machine and （） depend on effective lubrication. ["their no trouble period","their freely trouble period","its free trouble life","its trouble-free life"]
（）is a term denoting the determination of a ship’s position by observations of Celestial or terrestrial objects，or by a combination of both． ["Course-planning","Position-fixing","Radar-plotting","Stowage-plan making"]
荡桨时，采用方式（）旋回圈最小。 ["操满舵","满舵配合一舷桨向前，另一舷桨挡水","满舵配合一舷桨向前，另一舷桨向后"]
简述色素细胞瘤。
在计算机应用中，利用计算机帮助设计人员进行产品设计和工程设计等工作的计算机辅助系统是（）。 ["CBE","CAM","CAT","CAD"]
什么是药理学？
