finished

Răng được bảo vệ bởi lớp men cứng, dày khoảng 2mm. Lớp men này là hợp chấtCa5(PO4)3OH và được tạo thành bằng phản ứng: 5Ca2+ + 3PO43- + OH- → Ca5(PO4)3OH (1) Quá trình tạo lớp men này là sự bảo vệ tự nhiên của con người chống lại bệnh sâu răng.

My favorite store is the Stationery store for students. it's also quite close to my school about 1km to get there. here often sell school supplies such as: pens, books, notebooks, erasers, rulers, notebooks, pen boxes, there are some things that students like such as keychains, snow needles, teddy bears, .... I think the store is very good because this store has half of these school supplies so that students don't go to a faraway place to buy for study use but they forget or lose them. This store is also extremely clean. The aunt and uncle in the store are very friendly to help the students with anything.

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