Answer:
Option A is the correct answer.
Explanation:
The main ideas refer to the most important idea in a text; they are used to build the text around them with supporting ideas. In this case, the main idea is walking is not the most exciting form of exercise a person can take on for fitness. It is <u>explicit because it is directly stated in the paragraph</u>. Supporting ideas such as the description as a "simple activity" or the few things needed for this.
I think the statement that correctly uses commas is, "Tony thought the problem seemed simple. After working on it for an hour, however, he changed his mind." In this statement, it clearly sends the message that after Tony worked on the problem for an hour, he concluded that is was not an easy problem.
