一个比例，已知两个内项的和是28，差是12，两个比的比值是4，写出这个比例?
32：8=20：5或80：20=8：2
选修4－1：几何证明选讲
如图，已知点C在圆O直径BE的延长线上，CA切
圆O于A点，DC是∠ACB的平分线并交AE于点F、交
AB于D点，则∠ADF=？
Sam his homework in his room now.[ ]
A. does
B. doing
C. is doing
D. do
