选择A
do someone good 表示“对某人又好处”,等同于do good to someone
整句话的意思就是：去海边旅行会对你有好处.
其中B的be good with someone意为“与……相处得好”；C中“be well to"不是一个固定搭配,当然有时也可以这么用：“It would be well to start early.“表示最好还是早点动身；D中应该是do good to you.