The selection of English teachers used to be mainly based on ______.

A．the investigation of the life cycle of a protozoon is undoubtedly pure research
B．pure scientists tend to look down upon applied investigation
C．the discover of X-rays was made in applied research
D．the classification of research into "pure" and "applied" is neither accurate nor impersonal

A．it is a kind of prearranged investigation
B．no new knowledge can arise from applied research
C．it is more difficult to get results in applied research than in pure research
D．no specific scientific ability is needed in applied researc