a, He is getting fat because he eats junk food regularly.

b, Nam was absent from class yesterday because he had a fever.

c, My mother has donated food to homeless people because she wants to make them happy.

d, I work hard because I want to be a good student.

e, The students tidy the schoolyard every day and they don't litter because they want their school to look beautiful.

f, We try to behave well to other people because they want to have a good relationship with them.

----------

Giải thích: Mệnh đề (kết quả) + because + mệnh đề (nguyên nhân) = Because + mệnh đề (nguyên nhân), mệnh đề (kết quả).

I.

$\text{a.}$ He is getting fat, because he eats junk food regularly.

$\text{b.}$ Nam was absent from class yesterday, because he had a fever.

$\text{c.}$ My mother has donated food to homeless people, because she wants to make them happy.

$\text{d.}$ I work hard, because I want to be a good student.

$\text{e.}$ The students tidy the schoolyard every day and they don't litter, because they want their school to look beautiful.

$\text{f.}$ We try to behave well to other people, because we want to have a good relationship with them.

$\text{* Because:}$ Bởi vì

$\text{→}$ Chỉ nguyên nhân

$\text{→}$ Clause 1(result) + Because + Clause 2(reason)