Which of the following arguments is valid?

1. A.

   {p → q, r → s, r ∨ p, ¬q} ⊢ p

2. B.

   {p → q, r → s, r ∨ p, ¬q} ⊢ q

3. C.

   {p → q, r → s, r ∨ p, ¬q} ⊢ ¬r

4. D.

   {p → q, r → s, r ∨ p, ¬q} ⊢ s

Attempted by 34 students.