[General] I will keep doing it/this/that

[BloodSweatTears]

I am not sure what is the best word for my sentence below:

1- I am taking English lessons and I will keep doing this until I am happy with my English.

2-I am taking English lessons and I will keep doing that until I am happy with my English.

3- I am taking English lessons and I will keep doing it until I am happy with my English.

 

[bhaisahab]

They are all possible.

 

[BloodSweatTears]

They are all possible.

Do they convey any differences in meaning?

 

[emsr2d2]

You can also say "... I will keep doing so until ...". It means the same as the other three.