Complete these sentences using the verbs in brackets in the passive voice. A lot of TV stations (to build) in 1950s and television became very popular.

1. The sentence requires the past passive form of 'to build'.
2. The subject 'A lot of TV stations' is plural.
3. The past passive is formed with 'was/were' + past participle. The past participle of 'build' is 'built'.
4. Therefore, the correct form is 'were built'.