16. 如图,在长方体ABCD−A1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}ABCD−A1B1C1D1中,若EEE,FFF,GGG,HHH分别是棱A1B1A_{1}B_{1}A1B1,BB1BB_{1}BB1,CC1CC_{1}CC1,C1D1C_{1}D_{1}C1D1上的动点.且EH//FGEH//FGEH//FG,则必有((( )))