Which of the Following Are Conjugate Acid-Base Pairs in the Acid-Base

Multiple Choice

Which of the following are conjugate acid-base pairs in the acid-base reaction between ethanamine and water? CH₃CH₂NH₂ (aq) + H₂O (l) ⇌ CH₃CH₂NH₃⁺ (aq) + OH^- (aq)
I.H₂O and CH₃CH₂NH₂
II.H₂O and OH^-
III.CH₃CH₂NH₂ and CH₃CH₂NH₃⁺
IV.CH₃CH₂NH₃⁺ and OH^-

A) I only
B) I and IV
C) II only
D) II and IV
E) II and III