题目

In the shadow of Kenya’s Mount Kilimanjaro, nine Rothschild giraffes, the rarest giraffes on the planet, are free to wander at the English-style manor (庄园). Every day shortly before 9am, they come up to the house and stick their heads through the windows and doors in search of morning treats. The manor’s owners, Tanya and Mikey Carr-Hartley, share their dining table with them. And now the couple are sharing the fantastic experience with the public by opening the manor gates to guests at the giraffe hotel, the only hotel of its kind in the world. Now, guests can feed the giraffes at bre如图，已知：l1∥l2∥l3，AB=6，DE=5，EF=7.5，则AC=__．