11.如图,一块矿石晶体的形状为四棱柱ABCD−A1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}ABCD−A1B1C1D1,底面ABCDABCDABCD是正方形,CC1=2CC_{1}=2CC1=2,CD=3CD=3CD=3,且∠C1CB=∠C1CD=60∘\angle C_{1}CB=\angle C_{1}CD=60\circ∠C1CB=∠C1CD=60∘.则向量A1C→\overrightarrow{A_{1}C}A1C的模长为((( )))