题目

No sooner had he got home than he ____his coat and sat down at the table. A. threw off             B. threw out        C. threw about      D. threw sway 答案：A 三棱锥A－BCD，AB＝a，CD＝b，∠ABD＝∠BDC，M，N分别为AD，BC的中点，P为BD上一点，则MP＋NP的最小值是________．