明显是D.
你将原句简单化：He went on with his education with the money he saved.
On 和 in 明显不对,希望你还不至于在这两个之间徘徊.
By是通过某种手段,e.g He got the money by deceiving.
多读多记是解决这种问题的最好办法,切忌用中文思维将英文翻译过来.