Most people achieve financial security through
a. saving and investing
b. inheritance
c. a successful business that they own
d. working at a job or series of jobs

I would say A.

B would be incorrect as most people don't have inheritance money. It wouldn't help you achieve financial security, either.

C could be correct, but not many people own successful companies.

D would be OK, but, unless you have a contract, you could lose your job fairly quickly.

A makes the most sense. You can set aside money for emergencies, etc.

99, multiply all the sides