Second question, ∠ADE=∠B, congruence angle is ∴DE//BC, ∠ dec = 100, ∠C is congruence angle =80 degrees.

The third question, ab∨CD, ∴ Angle D and Angle A are complementary, ad∨BC, ∴ Angle A and Angle B are complementary, ∴∠B=∠D (complementary angles of the same angle are equal).