B4

The first heated swimming pool was constructed by Gaius Maecenas of Rome in the first century BC.
(past simple passive,т.к. он был построен, а не он построил. Действие произошло в определённый момент в прошлом.)

CONSTRUCT

B5

Swimming pools became popular in Britain in the beginning of the 19th century. By 1837, London authorities had built six indoor pools with diving boards.
(past perfect, т.к. действие завершилось к 1837 году.)

BUILD 

B6

The oldest surviving swimming club in the world is the Arlington Baths Club in Glasgow. It is still an active club and continues to own its original Victorian building with a large pool.
(степень сравнения)

OLD

B7

After the start of modem Olympic Games in 1896, the popularity of swimming pools took off. Nowadays there are lots of different swimming pools, both public and private.
(past simple,т.к. действие произошло в определённый момент в прошлом)

TAKE

B8

Most children enjoy swimming and swimming pools with their wave-making machines, water slides and tropical vegetation are something unique for them.
(child – ед.ч,  children – мн.ч.)

CHILD 

B9

If they could, kids would choose to spend their entire summer in the swimming pool.
(2й conditional)

CHOOSE

B10

However, not everyone has their own backyard pool.
(для he, she, it (3елицо), everybody, nobody, everyone, no one - мыиспользуем has)

HAVE