Both (a) and (b). In case of isogamy, the gametes can be flagellated and similar in size (in Chlamydomonas) or non-flagellated (non-motile) but similar in size (as in Spirogyra)
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.