1.study

2.play

3.to do

1.Are you free next sunday?

2.I have collected a lot of stamps from foreign countries so far.

4n+ 3 chia hết cho 2n+1 

=> 4n+2+1 chia hết cho 2n+1 

=> 2.(2n+1) +1 chia hết cho 2n+1 

=> 1 chia hết cho 2n+1 

=> 2n+1 = -1;1

=> 2n = -2;0

=> n= -1;0

Vì n là số tự nhiên => n=  0

1,was

2,have watched

3,went

4,have...been

5,is waiting

with