determine whether the given argument is valid or invalid. If it is invalid, select a counterexample.
-1. (?x)(Ax ? Bx) ? (?x)Cx
2) (?x)(Ax • ?Bx)
3) (?x)(Dx ? Bx) / (?x)(Dx ? Cx)
A) Valid
B) Invalid. Counterexample in a domain of 2 members, in which:

\begin{array} { l l l l } \text { Aa: True } & \text { Ba: False } & \text { Ca: False } & \text { Da: False } \\\text { Ab: False} &\text { Bb: True } &\text {Cb: False }&\text { Db: True } \\\end{array}

C) Invalid. Counterexample in a domain of 2 members, in which:

\begin{array} { l l l l } \text { Aa: True } & \text { Ba: False } & \text { Ca: False } & \text { Da: False } \\\text { Ab: True} &\text { Bb: True } &\text {Cb: True }&\text { Db: True } \\\end{array}

D) Invalid. Counterexample in a domain of 2 members, in which:

\begin{array} { l l l l } \text { Aa: False} & \text { Ba: False } & \text { Ca: False } & \text { Da: False } \\\text { Ab: False} &\text { Bb: True } &\text {Cb: False }&\text { Db: True } \\\end{array}

E) Invalid. Counterexample in a domain of 2 members, in which:
Aa: True Ba: False Ca: False Da: False Ab: True Bb: False Cb: False Db: True

1. (∃X)(Gx • ∼Hx) ≡ (∃X)(Hx • ∼Ix)

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