Can/Could and Be able to.

[hoangkha]

Hi!
1- I'm sorry that I ............... phone you yesterday because I had a lot of things to do.
A- was not able to (key)
B- could not
2- I ................... play football now, but when I was young I ................. play very well.
A- cannot/could (key)
B- am not able to/was able to
Why isn't B chosen in the above sentences, please?

[billmcd]

Who said or where did you read that "A" is the only possible answer?

[hoangkha]

Who said or where did you read that "A" is the only possible answer?

They are from exercises. Of course.

[Tdol]

It's based around the idea that was able to is better for a single occasion, but this is not a rule and in many cases either form can be used.