If a system contains 1,000 disk drives, each of which has a 750,000- hour MTBF, which of the following best describes how often a drive failure will occur in that disk farm:

a. once per thousand years
b. once per century, once per decade
c. once per year, once per month
d. once per week
e. once per day
f. once per hour
g. once per minute
h. once per second