`1.` Mastering English is necessary.

- It is + adj + (for sb) + to V

-> V-ing + is + adj + (for sb): Làm gì đó là ...

`2.` It took the writer twenty years to write his best-selling novel.

- S + spend(s)/spent + time + V-ing

-> It + takes/took + O + time + to V: Ai đó mất bao nhiêu thời gian để làm gì đó

`3.` He isn't old enough to take part in the excursion.

- S + tobe + too + adj + (for sb) + to V

-> S + tobe + not + adj (trái nghĩa) + (for sb) + to V: không đủ ... để làm gì đó

- young (a): trẻ >< old (a): già

`4.` The luggage was too heavy for her to carry it upstairs.

- S + tobe + so + adj + that + S + V

-> S + tobe + too + adj + (for sb) + to V: quá ... đến nỗi không thể làm gì đó

`5.` He is looking forward to hearing from his long-lost brother.

- look forward to + V-ing: mong chờ làm gì đó

- Thì HTTD: (+) S + is/am/are + V-ing