课本中的例题 ,大部分都具有典型的导向作用 ,许多中考试题源于此又高于此 ,所以同学们要重视课本例题的学习 .例 1　 ( 2 0 0 2年海南省中考题 )已知 :如图1 ,AB是⊙O的直径 ,BE是⊙O的切线 ,切点为B .点C为射线BE上一动点 (点C与点B不重合 ) ,且弦AD平行于OC .( 1 )求证 :CD? Most of the sample questions in the textbooks have a typical guiding role. Many of the examination questions originate here and are higher than this. Therefore, the students should pay attention to the study of textbook examples. Example 1 (in Hainan Province in 2000) : As shown in Figure 1, AB is the diameter of ⊙O, BE is the tangent of ⊙O, and the point of tangency is B. Point C is a point on the ray BE (the point C does not coincide with point B), and the string AD is parallel to the OC. 1) Verification: CD?