Answer: A. to provide more information
Step-by-step explanation:
In this case, an estimate of the number of people who attended theater is given in the parentheses. This means that the words in parentheses provide more information about the increase of people. These words do not emphasize new ideas, or explain terms or a difficult concept - they just provide additional information about the idea which is already introduced at the beginning of a sentence. The correct answer is, therefore, A.