1/It is 5 days since he left.

=>He has left for 5 days

2/Opening the window is difficult.

=> it is dificult to open the window 

3/Listening to her songs is happy.

=> it is happy to listen to her songs

4/Answering this question is difficult.

=> it is dificult to answer this question 

5/It is easy to drive a car.

=> driving a car is easy

6/It is important to take a break at least twice a day.

=> taking a break at least twice a day is important

7/Doing this exercise is not difficult.

=>it is not dificult to do this exercise

8/Doing English everyday is necessary.

=> it is necessary to do English (?) everyday

9/It is interesting to talk to you.

=> talking to you is interesting

10/It is difficult to learn Japanese.

=> learning Japanese is difficult 

Công thức chung:

It is + adj + to V + O

--> Ving + O + is + adj

`1` He hasn't left for 5 days

`-` It's + thời gian trong quá khứ + since + S + (last) + Ved/V2

`-` S + has/have + not + Ved/V3 ...

`2` It is difficult to opening the window

`3` It's happy to listening to her songs

`4` It's difficult to answer this question

`5` Driving a car is easy 

`6` Taking a break at least twice a day is important

`7` It's not difficult to do this exericse

`8` It's necessary to do english every day 

`9` Talking to you is interesting

`10` Learning Japanese is difficult

`@` Công thức từ câu `2` `->` câu `10`.

`-` Ving + ... + is + adj (tính từ)

`-` It's + adj + (for sb) + to Vinf : như thế nào (cho ai) làm gì đó