Here you’ve got the answers:

1-a-true

2-a-black

3-c-picadilly

4-b-the serpentine

5-c-buckingham palace

6-c-nelson

7-c-london bridge and tower bridge

8-a-regents park

9-b-tate  modern

10-a-kensington gardens

11-d-black

12-a-hyde park

13-b-whitehall

14-a-beefeaters

15-c-oxford street

16-c-all of them

17-d-northern line

18-b-waxworks

19-a-globe

20-b-eros

21-b-a cathedral