Дополните предложение нужной формой глагола. On Sundays my parents stay at home and... a lovely time watching TV.

The correct answer is 'have'. The full sentence is: On Sundays my parents stay at home and have a lovely time watching TV.

The verb 'have' is used here to express the idea of experiencing something or spending time doing something. In the context of spending time, 'have a lovely time' is an idiomatic expression. The subject 'my parents' is plural, so we need the base form of the verb and not the 'has' form.