What are the four chemical agents recognized?

The recognized categories of chemical agents include blood agents, blister agents, choking agents, and nerve agents. Blood agents affect the bodily functions primarily through the bloodstream, often interfering with oxygen transport, while blister agents cause severe skin and mucous membrane damage upon exposure. Choking agents typically target the respiratory system, causing harm through inhalation, and nerve agents disrupt the nervous system, leading to incapacitation or death.

Among the provided options, the combination of blood, blister, choking, and nerve agents accurately reflects the established classifications used in military training and chemical warfare studies. The other choices include inaccuracies, such as the use of "irritant" or "tear," which do not represent the recognized major categories of chemical agents in this context. Therefore, option B stands out as the appropriate selection, encapsulating the critical aspects of the various types of chemical agents that Marines must be aware of when discussing battlefield scenarios involving chemical warfare.