单选题 His father had promised to buy him a computer______ he behaved himself.
【正确答案】 D
【答案解析】解析：句意：他的父亲许诺，如果他循规蹈矩就会给他买一台电脑。provided作连词，引导条件状语从句表示“如果，假如”，behave oneself意为“表现良好”。故本题答案为D。