Which of the following is not an advantage of friction?

The friction between two surfaces does not depend on one of the following. This one is:

If the sliding friction between two surfaces is found to be 8 N, then the static friction between these two surfaces is most likely to be:

Which of the following statements is incorrect ?

If the static friction between two surfaces X and Y is found to be 20 N, then the rolling friction between these two surfaces should most likely be :