In this question, we have to find which of the options represents a conjugate acid - base pair.
The definition of a conjugate acid is a molecule that received a H+ from the surroundings and becomes more electropositive, usually represented with the + sign.
A conjugate base will do the opposite, will be a molecule that releases a H+ to the surroundings, receiving a - sign
The option that best represents this pair is NH4+, that received one H+, and NH2-, which released a H+, letter D