14. The boys ... TV when their mum came home. a) were watching b) had been watching c) had watched

Перевод задания: Мальчики ... телевизор, когда их мама пришла домой.

a) were watching — The boys were watching TV when their mum came home. (Мальчики смотрели телевизор, когда их мама пришла домой.)

Past Continuous обозначает действие, которое происходило в момент другого события в прошлом.