Different between si unit and derived unit

There are seven base SI units corresponding to different parameters and are considered independent of each other. Derived units are derived from these 7 base units. Derived units are dependent on the base units and are not independent of each other. For example, let us derive the SI units for force. By Newtons Second Law of Motion, the force is same as the product of mass and acceleration of a body. that is, force = mass x acceleration. Also, acceleration is defined as the rate of change of velocity. And velocity is defined as the rate of change of displacement. Thus, force = mass x acceleration = mass x dv/dt = mass x dt2 Mass has SI units of kg, distance is measured in m and t has the SI unit of second. Thus, Sl unit of force is kg.m/s^2 (also known as Newton).

the answer is b, have negligible mass