IF SOMEONE KNOCKS ________ THE DOOR _________ NIGHT, DON’T OPEN IT...

28. - DE KIEM TRA ANH VAN SO 1HOT
DE KIEM TRA ANH VAN SO 1HOT

28. If someone knocks ________ the door _________ night, don’t open it.

a. at/at

b. on/at

c. up/in

d. at/on