some question about choose best answer 1.The polit lose contact with the military base, [ D ]the plane crashed in the desert. A.by means of which B.for which C.among which D.as a result of which Right D I choose B 2.These students will graduate from the university next summer, [ D ] they will have studied here for four years. A.by then B.by that time C.by what time D.by which time Right D I choose B Please tell me why I need to choose the answer D.