How long does a large generator take to come up, when supplying power to the entire building?

How long does a large generator take to come up, when supplying power to the entire building?

A.
10 minutes or longer.

B.
5 to 10 seconds.

C.
5 minutes or longer.

D.
15 to 20 minutes.

Explanation:
A generator large enough to supply power to an entire organization, or building, can take 10 minutes or longer to reach a stable 60 Hz and 110V. In the

meantime, a correctly sized UPS that can function throughout the time period required for the generator to stabilize is needed to protect the server.
References:
Charles J. Brooks, Server+ Certification Exam Cram 2 (Exam SK0-002), QUE Publishing, Indianapolis, 2006, pp. 227-240.