Walking is not the most exciting form of exercise a person can take on for fitness. Yet it is low impact and requires no fancy equipment. That makes walking a simple activity for those new to exercise. Walking is less likely than other exercises to cause injury to leg tendons and muscles. All it requires is a good pair of sneakers—no cables, stylish outfits, or weights required. Of course, a person could increase the benefit of a workout by adding weights or speed walking.

Identify the main idea of this paragraph.

Walking is a difficult and safe exercise for beginners.
Walking is an easy and safe exercise for beginners.
Walking is a boring and dangerous form of exercise.
Walking is an exciting and very effective form of exercise.