Isosceles trapezoid ABCD has parallel sides AD and BC, with BC<AD and AB=CD. There is a point P in the plane such that PA=1,PB=2,PC=3, and PD=4. What is ADBC?<spanclass=′latex−bold′>(A)</span>41<spanclass=′latex−bold′>(B)</span>31<spanclass=′latex−bold′>(C)</span>21<spanclass=′latex−bold′>(D)</span>32<spanclass=′latex−bold′>(E)</span>43