WHAT DOES THE WORD ‘THEIR’ IN LINE 3 REFER TO

28. - BAI TAP TIENG ANH LOP 8 UNIT 7 NEIGHBORHOOD CO DAP AN SO 2
BAI TAP TIENG ANH LOP 8 UNIT 7 NEIGHBORHOOD CO DAP AN SO 2

28. What does the word ‘their’ in line 3 refer to?

a. cities

b. countries

c. houses

d. suburbs