题目

We may all have had the embarrassing moment：Getting half­way through a story only to realize that we've told this exact tale before to the same  person. Why do  we  make  such  memory mistakes? According to the research published in Psychological Science, it may have to do with the way our brains process different types of memory. Researchers Nigel Gopie, of the Rotman Research Institute in Toronto, and Colin Macleod, of the University of Waterloo, divided memory into two kinds. The first was source memory，or the ability to keep track of where information is coming from. The设a，b是平面α内两条不同的直线，l是平面α外的一条直线，则“l⊥a，l⊥b”是“l⊥α”的（ ）A．充要条件B．充分而不必要的条件C．必要而不充分的条件D．既不充分也不必要的条件