on 的固定词组：
(1) on Sunday (2) on duty
(3) on Christmas (4) on one's birthday
(5) on one's way to(6) on the tree
(7) on the left (8) on the east of
(9) on foot (10)on behalf of
(11)on time (12)on and on
(13)on business (14)on leave
(15)on the back (16)on watch
(17)on the corner (18)on purpose
(19)on the contrary(20)on the opposite of
(21)on show (22)on sale
51.keep on...52.hold on...
53.insist on...54.rely on...