题目

Teachers have spend ________ Teachers' Days so far.It is the ________ Teachers' Day on September 10, 2016. A．thirty­one; thirty­two  B．thirty­one; thirty­second C．thirty­first; thirty­two  D．thirty­first; thirty­second 答案：B已知空间四边形ABCD中，O是空间中任意一点，点M在OA上，且OM=2MA，N为BC中点，则=（ ）A．B．C．D．