Tantamount

The word "Tantamount" is an adjective that implies the idea of being equivalent in seriousness to, or virtually the same as, something. While "tantamount" was used as a verb or a noun in its archaic form, the more common and modern usage is as an adjective.

Option A: ["To leave a pet home alone is tantamount to cruelty."] uses tantamount correctly; here, leaving a pet alone is presented as equivalent to cruelty. Option B: ["Overlooking state norms tantamounts to a crime." ] is also correct, although old-fashioned, it uses tantamount as a verb, equating overlooking state norms with crime.  Option C: ["His refusal to answer was tantamount to an admission of guilt." ]is also correct, as refusal is equated to an admission of guilt. 

Hence, the correct answer is Option D ( All are correct).