Which sentence is the most correct, clear, and concise?
Select one:
a. In order to achieve a life that is both successful and rewarding, individuals must focus on developing one set of skills that they can sell and many outside interests. 
b. In order to live a life that is both successful and rewarding, one must develop a particular skill that is in demand by the marketplace and diverse outside interests to amuse one throughout life. 
c. For a successful, rewarding life, an individual must develop a marketable skill and diverse interests. 
d. To have a successful, rewarding life, individuals must develop particular, marketable skills, and they also must explore diverse interests.