a. He will start drinking, which we don't want.
b. He will start drinking, which is something we don't want.
c. He will start drinking, which we don't want him to do.
d. He will drink, which we don't want him to do.
Are any of the above sentences grammatically correct?
Are any natural?
If '3' is correct, what does 'which we don't want him to do' modify?
Many thanks.