AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Option A — Both A and R are true, and R is the correct explanation of A.
The father is either XY; he passes X or Y to the child, while the mother (XX) always passes X, thus determining the child's sex.
The passage explicitly states: "the sex of the children will be determined by what they inherit from their father" — a child inheriting X from father is a girl, Y makes a boy. The mother always contributes X. So R directly and correctly explains A. Choose A.