Correct choice is (a) High- performance liquid chromatography (HPLC)
To explain I would say: In order to achieve the high resolutions characteristic of HPLC, stationary-phase particles 2-5 μm in diameter are commonly used. Because the particles are so small, HPLC systems are operated under high pressure (5-10 MPa) to achieve flow rates of 1-5 ml min -1. FPLC instruments are not able to develop such high pressures (1-2 MPa) and are therefore operated with column packings of larger size.