Existing installations are encouraged to
replace Halon 1301 with one of the substitutes listed.

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.

The correct answer is: when all of the elements of the business
have returned to normal functioning at the original site. Its important to remember that a threat to continuity exists when processing is being returned to its original site after salvage and cleanup has been done.

"The Clark-Wilson model is also an integrity-protecting model. The Clark-Wilson model was developed after Biba and approaches integrity protection from a different perspective. Rather than employing a lattice structure, it uses a three-part relationship of subject/program/object known as a triple. Subjects do not have direct access to objects. Objects can be access only through programs." Pg 347 Tittel: CISSP Study Guide