2.在长方体ABCD−A1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}ABCD−A1B1C1D1中,AB=2AB=2AB=2,AA1=AD=4AA_{1}=AD=4AA1=AD=4,EEE为C1D1C_{1}D_{1}C1D1的中点,则点AAA到平面B1CEB_{1}CEB1CE的距离为((( )))