Under Fair Housing regulations, reasonable modifications can be made to the unit:

The correct answer is that reasonable modifications can be made to the unit at the tenant's expense. This is in alignment with the Fair Housing Act, which stipulates that individuals with disabilities are allowed to make modifications to their living spaces to ensure accessibility. While tenants must cover the costs of these modifications, they are also protected by the right to live in a home that meets their accessibility needs.

In the context of the other options, modifications do not need to adhere to the condition of restoration upon moving out, as the law allows tenants to have modifications that can make a unit more livable for them, even if those changes are permanent. The mention of parking outside the entry to the clubhouse relates to modifications within the unit itself rather than general property management or community rules, and thus does not apply as a relevant condition for reasonable modifications under the Fair Housing laws. Therefore, the requirement of expense is the fundamental principle governing reasonable modifications.