题目

Do you know when and where the first republic ______ ? A. turned into realityB. existed C. come into action D. came into being   答案：Dcome into being 意为“产生，出现”。如图，在长方体ABCD-A1B1C1D1中，E、P分别是BC、A1D1的中点，M、N分别是AE、CD1的中点，AD=AA1=a，AB=2a．（1）求证：MN∥面ADD1A1；（2）求三棱锥A─PED体积的大小．