21 We ....... half the rubbish on the beach by the time Jeff arrived. A have cleaned up B had cleaned up C had been cleaning up

Solution:

• The sentence describes an action (cleaning rubbish) that was completed before another past action (Jeff arrived).
• This indicates the past perfect tense is required.
• "Had cleaned up" correctly uses the past perfect to show an action completed before another past event.

Answer: B had cleaned up