题目

My older brother and I are busy   61   (arrange) a trip to Africa. We will leave London on 15 July, and we’ll be flying to Morocco. We are going to travel on camels   62   the Sahara Desert. After the trip by camel, we’re going to travel down the River Nile. We’ll start at Lake Victoria. A little way down the river from Lake Victoria, the water   63   (actual) gets quite rough. So, we’ll go white-water rafting,   64   is quite dangerous, but very exciting! After white-water rafting, we’re going on a trip to see wild animals in Kenya.   65   we’ll be walking f如图，在梯形ABCD中，DC∥AB，∠D=90°，AD=4cm，AC=5cm，S梯形ABCD=18cm2，那么AB=（    ）cm．