Answer:
d. any agent used to bring about mass death, casualties, or massive infrastructural damage.
Step-by-step explanation:
This is the definition that best describes what a weapon of mass destruction is. A weapon of mass destruction (WMD) is a type of weapon that brings about mass death, casualties or massive damage to human infrastructure, natural structures or the biosphere. The word is used more in a political sense than in a technical sense, as there is no universal agreement on what weapons would be considered WMD.