In which sentence is the appositive phrase punctuated correctly?

A. Shakespeare the great writer, penned many famous sonnets.
B. Shakespeare, the great writer, penned many famous sonnets.
C. Shakespeare, the great writer penned many famous sonnets.
D. Shakespeare the great writer penned many famous sonnets.

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.