Judy Blume's career as an American writer spans four decades and includes many literary awards. She is most famous for her novels geared toward pre-teens. One notable example is Tales of a Fourth-Grade Nothing. However, Blume also has had success writing for an adult audience. Three of her novels for adults reached the New York Times best-seller list. In a 2008 interview Blume remarked, "I have so many stories left to tell!" By that time she had written nearly 30 novels. Judy Blume is an exceptionally talented and productive American author. Identify the main idea of this paragraph.

Judy Blume has been writing for a very long time. (explicit)
Judy Blume has been writing for a very long time. (implicit)
Judy Blume has been a very busy and gifted writer. (explicit)
Judy Blume has been a very busy and gifted writer. (implicit)
How does the third sentence ("That makes walking...") support the main idea of the paragraph?

It points out that walking is a good introduction to exercise for beginners.
It says that walking is too easy for people who have experience with exercise.
It points out that beginning exercisers may not like walking because it is too easy.
It says that walking is less costly than other activities because it needs no equipment.