试述地理坐标系的定义及其类型。
参考答案：
地理坐标系——就是用经纬度表示地面点位的球面坐标系。在大地测量中，又分为天文坐标系、大地坐标系和地心坐标系。
萃取操作包括若干步骤，除了（）。
A、原料预热
B、原料与萃取剂混合
C、澄清分离
D、萃取剂回收
Upon receipt of a distress message，a merchant vessel is bound to proceed to the scene of the distress. Under which of the following cases would this NOT be true?（）
A.The vessel would arrive at the distress scene more than 36 hours after the receipt of the initial distress message
B.There are vessels closer to the distress scene that are proceeding to assist
C.The Master of the vessel in distress has requisitioned another vessel，and that vessel has accepted the requisition
D.You are on a tanker and the distress involves a major fire on board the other vessel
