∫AB∨CD。

∴∠ A +∠ ADC = 180 (two straight lines are parallel and the internal angles on the same side are complementary).

∫∠A =∠C

∴∠ C +∠ ADC = 180 (equivalent substitution)

∴ad∨CB。 (The internal angles on the same side are complementary, and the two straight lines are parallel)

∴∠ E =∠ F. (Two straight lines are parallel and the internal dislocation angles are equal)