题目

.He went to American _____some English as well as ____.     A. learning ,to travel  B. learning,  traveling  C. to learn, travel     D. to learn ,to travel 答案：D如图，△ABC为边长是5的等边三角形，点E在AC边上，点F在AB边上，ED⊥BC，且ED=AE，DF=AF，则CE的长是A.B.C.20+10D.20-10