Is the least expensive because it is basically a structure with power and would be the most difficult to test because you would have to install all of the hardware infrastructure in order for it to be operational for the test.
The following answers are incorrect:
non-mobile hot site. Is incorrect because it is more expensive then a cold site and easier to test because all of the infrastructure is in place.
mobile hot site. Is incorrect because it is more expensive then a cold site and easier to test because all of the infrastructure is in place.
warm site. Is incorrect because it is more expensive then a cold site and easier to test because more of the infrastructure is in place.