读图回答下列问题。（共9分）

(1)要在海边建油港码头，应建在A处还是B处?为什么?  (3分)
                                                                                  
                                                                                  
                                                                                  。
(2)欲从油矿区向油港铺设输油管道，线路如图中虚线所示，请说明理由。(2分)
                                                                                 
                                                                                 
                                                                                 。 
(3)C、D两地高程相等,从C地登上甲山顶，有什么有利和不利条件?
                                                                                 
                                                                                 
                                                                                  。
(4)B处在甲山顶的什么方向?          ，D、G两地的相对高度是多少?              。