A compound made up of A and B atoms have a crystalline structure ,in which A forms Hexagonal close packed structure and B occupies $\;\large\frac{2}{3}\;$ of octahedral holes .What will be the simplest molecular formula ?

Question

$(a)\;A_{3}B_{3} \qquad(b)\;A_{2}B_{3} \qquad(c)\;A_{3}B_{2} \qquad(d)\;A_{4}B_{3} $