The following sentence may contain a verb that merely implies causation. Choose the version in which the verb clearly expresses cause and effect. If the original sentence is correct, select c. no change.

The author argues that the problem also results from the sale of complimentary copies of textbooks.
a.
The author argues that the problem also takes place following the sale of complimentary copies of textbooks.
b.
The author argues that the problem also happens from the sale of complimentary copies of textbooks.
c.
no change