题目

A drink of water is just a matter of turning on a tap for most of us. However, water for those in drought-stricken northwestern China can’t be taken for granted. Its present shortage is a matter of life and death to them. The tragedy is the direct result of the drought that has hit a large area of northwestern China, and is affecting more than 50 million people. The drought began last spring, ravaging Gansu, Qinghai and Shaanxi. Experts say the drought is a result of less rainfall, insufficient water reserves, high temperatures, dated irrigation projects, environmental damage and glo如图所示，多面体ABC-A1B1C1是由直棱柱被平面A1B1C1而成．其中AA1=4，BB1=2，CC1=3，AB与BC垂直，AB=BC=1（1）在A1B1上是否存在一点D1，使得C1D1平行于平面ABC．（2）求二面角B1-A1C1-A的大小．（3）求该多面体的体积．