Cloose the right variant two years derry bought a car. a) ago b) for c) sinse

everyone agrees that unless tiger population is protected ,they will become extinct.if it were not the efforts made by international campaigns the extinction would already have become a fact.it is time to cooperate and help to animals otherwise the future will be sad.supposing there were no tigers left in the world: how would we all feel? !

1. i exercise regularly in summer but more to do in winter. 2. she usually walks slowly but now she is walking even   faster . 3. nina speaks loudly but mary speaks even   louder . 4. he runs fast, than other boys. 5. i don’t sleep enough, less   than 8 hours. 6. he behaves badly, than other boys. 7. i smile often, more than my sister. 8. peter lives far from school, but ann lives closer .

я думаю, что  4 и в 6 предложениях ничего изменять не надо. может я ошибаюсь.