6. On Sundays, tea (SERVE) on the coffee table in the living room — it was their family tradition.

Solution:

The sentence describes a habitual action in the past ('was their family tradition'). The verb 'SERVE' needs to be in the past tense, and since it's an action done to the tea, it should be in the passive voice. 'Tea' is singular, so the past passive form is 'was served'.

Answer: 6. On Sundays, tea was served on the coffee table.