19.( 1)E is a point on the semicircle, so AE⊥BE (theorem), AD⊥ABE, so DAE⊥ABE, BCE⊥ABE, so ADE⊥BEC.

(2)CD∨AB, then AB∨DFEC, CD∨ABEF, then CD∨EF.

(3) If parallel lines of AF are drawn along E, and the intersection of AB is E', then AE' = EF =1= AB/2 = BE' =1,AF=EE'=BE=AB/2= 1, and the angle ABE=60, then