Final answer:
The argument is valid because it follows the rule of inference known as Modus Ponens.
Step-by-step explanation:
To determine the validity of the given argument, we need to apply the rule of inference known as Modus Ponens. This rule states that if we have a premise of the form 'P ⊃ Q' and another premise that is the affirmative form of the antecedent 'P', then we can validly conclude the consequent 'Q'.
In the given argument, the first premise is 'G ∨ ∼T' and the second premise is '(G ⊃ ∼H) • (∼T ⊃ A)'. By applying Modus Ponens, we can derive the conclusion (∼H ∨ A).
Therefore, the reasoning in the given argument is valid, so the correct answer is a. MP - valid.