Considere a seguinte demonstração para o teorema left parenthesis P rightwards arrow Q right parenthesis logical and left parenthesis Q rightwards arrow R right parenthesis rightwards arrow left parenthesis P rightwards arrow R right parenthesis.

1. P rightwards arrow Q hip.

2. Q rightwards arrow R hip.

3. P hip

4. Q 1,3, modus ponens

5. R

Assinale a alternativa que justifica a validade do item 5.

a.
2,4, modus ponens.

b.
2,4 tautologia.

c.
2,4, modus tollens.

d.
modus ponens.

e.
2,3 modus tollens.