she last worked in this company three years ago

=> It is

Nga works more carefully than Mr.Thanh does

=> Nga is

`1` It is three years since she last worked in this company .

`-` It is + time + since + S + last + V(quá khứ) + O : Đã bao lâu kể từ khi ai đó lần cuối làm gì .

`2` Nga is a more carefully worker than Mr.Thanh .

`-` So sánh hơn danh từ với tính từ .

`@` S1 + be + (a/an) + more + adj + N + than + S2 .

`1.` It is three years since she last worked in this company

`-` S + last + V2/ed+ O + time

`=` It is + time + since + S + last + V2/ed + O

`->` đã bao lâu kể từ lần cuối ai làm gì

`2.` Nga is a more careful worker than Mr.Thanh 

`-` S + V + (more) + adv_(er)  + than + S

`=` S + tobe + (a/an) + adj + N + than + S