Viết các câu sau thành câu bị động
3. There was plentiful plastic litter on the platform.
4. We clapped after the pricipal gave the greetings.
5. When the climate is fine, we often climb up the cliff and have a pleasant picnic.
6. His presentation about green lifestyle is really gripping.
7. The grammar notes are practical for US to understand primary issues.
Giúp mình với ạ!