as to

[azz]

a. There are so many variables as to the outcome of these games that it is impossible to make predictions.
b. There are so many variables regarding the outcome of these games that it is impossible to make predictions.


c. There are so many variables as to these games that it is impossible to make predictions.
d. There are so many variables regarding these games that it is impossible to make predictions.

Are the above sentences grammatically correct?

Many thanks

[Alan]

Yes, except (c).