He's looking forward to 3 (go) on a beach clean-up next weekend. He can't stand 4 (see) plastic rubbish in the sea! When he leaves school, Adam would like 5 (work) with animals. He wants 6 (be) a vet.

Решение:

• 3. He's looking forward to going on a beach clean-up next weekend. (После фразы 'looking forward to' используется герундий '-ing').
• 4. He can't stand seeing plastic rubbish in the sea! (После глагола 'can't stand' используется герундий '-ing').
• 5. When he leaves school, Adam would like to work with animals. (После модального глагола 'would like' используется инфинитив с частицей 'to').
• 6. He wants to be a vet. (После глагола 'wants' используется инфинитив с частицей 'to').

Ответ: going, seeing, to work, to be