单项选择题 The main steering gear must be able to steer the ship at maximum ahead service speed and be capable at this speed, and at the ships deepest service draught, of putting the rudder from 35 degrees on one side to 30 degrees on the other side within no （）.

单项选择题 Which of the following chemicals will be used where protection against caustic cracking is required in boiler treatment?（）

单项选择题 Coalescence is the breakdown of surface tension between oil droplets in an oil/water mixture, which causes them to join and （） in size.