maintain 维护,保持.
如:maintain the system(维护系统)
stay 停留，呆在某地
如:stay at home(待在家)
keep 保持，保留 ,保管,记住
如:keep it on mind; keep the money for me.
hold 抓住,拥抱,暂停(某件事),
如:hold the handrail(抓住扶手);Hold me, Please! (抱抱我好吗);Hold the project暂停此项目, hold on(电话用语:稍等).
