please help me with these math questions!

Which of the following is the proper way to begin a proof by contradiction of the theorem "vp e Q, aq e Q, p # 0 - q = 1/p"? Suppose that some nonzero rational number is the reciprocal of some rational number O Suppose that every nonzero rational number is not the reciprocal of any rational number O Suppose that every nonzero rational number is the reciprocal of some rational number O Suppose there is some nonzero rational number that is not the reciprocal of any rational number Lemma 1: Vm EZ, Vn EZ, m # 0An# 0 - mn #0 Theorem: The difference of any two rational numbers is a rational number. Proof: Let m and n be any two arbitrary rational numbers 1. m = p/q, where PEZAqEZAq#0 2. n = ris, where rE ZASEZAS #0 3. m- n= p/q- rls 4. m - n = (ps - qr) / qs, where = (ps - qr) E ZA qs E ZA qs # 0 5. m- nEQ In the proof shown above, which step requires algebraic substition as its justification? Step 2 Step 4 Step 3 Step 5