Can you please check these sentences I'm doubtful about?

Thank you very much.

1) My parents like my clothing style because they think that wearing practical clothes is the most important thing/most important is to wear practical clothes/
2) I was given these trousers for my birthday Yesterday but they are too tight. Is it OK if I change them?
3) I'm afraid they were so popular that they've all been sold and I'm afraid we won't be supplied with any more by the manufacturers.

1 = fine

2 = no capital Y on "yesterday" - comma needed after "yesterday"

3 = Rephrase so that "I'm afraid" is used only once, not twice, and there's a comma after "sold."

Sure! I'd be happy to help you check these sentences. Here are my suggestions:

1) My parents like my clothing style because they think that wearing practical clothes is the most important thing/most important is to wear practical clothes.
- Both options are grammatically correct, but to determine which one is more suitable, it depends on the intended meaning. If you want to emphasize that wearing practical clothes is the most important thing overall, then the first option "wearing practical clothes is the most important thing" is better. If you want to emphasize that the most important aspect of clothing style is to wear practical clothes, then the second option "most important is to wear practical clothes" works better.

2) I was given these trousers for my birthday yesterday, but they are too tight. Is it okay if I exchange them?
- "Change" typically implies altering or modifying something, while "exchange" implies replacing one item with another. Since you mentioned that the trousers are too tight, it would be more appropriate to use "exchange" here.

3) I'm afraid they were so popular that they've all been sold, and I'm afraid we won't be supplied with any more by the manufacturers.
- This sentence looks fine. However, it's worth noting that you repeat "I'm afraid" twice in one sentence. If you want to avoid repetition, you can consider rephrasing it like: "Unfortunately, they were so popular that they've all been sold out, and we won't be receiving any more supplies from the manufacturers."

I hope this helps! Let me know if you have any more questions.