A Person Who Uses a Rule of Thumb to Determine

A person who uses a rule of thumb to determine the best rate of savings:

A) is necessarily making a mistake, since finding the best rate of savings involves complex mathematical models.
B) is necessarily making a mistake, since there is no single best rate of savings.
C) is not necessarily making a mistake because rules of thumb often arise out of trial and error or from observation of others' successful decisions.
D) is not necessarily making a mistake because, in the long run, all rates of savings turn out to yield the same economic benefit.