Correct option is (c) In monoadelphous, all filaments of stamens are bunched and all the stamens are united
The best I can explain: In epiphyllous flowers, stamens are attached to perianth. Stamens attached to carpels are gynandrous. In monoadelphous, all filaments of stamens are bunched and all the stamens are free. In polystemonous, stamens are free i.e. they are neither attached to any part of the flower nor to each other.