Điền từ hoàn thành đoạn văn

giải thích giúp mk vs ạ

Dear Parents,

It has been observed that many students are coming to (10)_______ school late. Please ensure that your child reaches school (11)______7:25am sharp. Students must also wear (12)_________school uniform.

Regards,

School Administration
11. A. an B. an C. the D. no article
12. A. on B. in c. of D. bty
13. A. proper B. properly c. properness D. propering