未分类题What can we infer from the passage?A.Over the last two decades, colleges altered the composition of their work force.B.In the past twenty years, the number of full-time instructors increased by 630,000.C.All the managerial positions added during the period from 1987 to 2007 were full time.D.There were altogether 614,000 teaching positions in the United States in 2007.