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如图,在直三棱柱\(ABC-A_{1}B_{1}C_{1}\)中,\(AB⊥BC\),\(AB=BC=1\),\(AA_{1}=2\),\(D\)是\(AA_{1}\)的中点.
\((\)Ⅰ\()\)求异面直线\(A_{1}C_{1}\)与\(B_{1}D\)所成角的大小;
\((\)Ⅱ\()\)求二面角\(C-B_{1}D-B\)的大小;
\((\)Ⅲ\()\)在\(B_{1}C\)上是否存在一点\(E\),使得\(DE/\!/\)平面\(ABC\)?若存在,求出\( \dfrac {B_{1}E}{EC}\)的值;若不存在,请说明理由.