Answer:
Step-by-step explanation:
1. as we (are)
2. it be they. Sounds weird but that is the correct agreement.
3. I think 3 is correct. The apostrophe is in the right place.
4. I, who am older, know better than you.
5. I don't see anything wrong with 5. You might want to rewrite it as Is there any reason why Arthur shouldn't go?
6. Everybody tried his (or her) hardest.
7. like those sorts of cakes.
8. Venus is a planet. There is nothing wrong with the sentence.
9. This is a very odd rule of grammar. It should be I wish I were a clown.