Fill in the blanks by reasoning; As shown in figure 1, if ∠ 1=∠2, then (DC)÷(AB) causes (internal dislocation angles are equal and two straight lines are parallel).

If ∠ DAB+∠ ABC = 180, then (AD) ∠ (BC) causes (the inner angles on the same side are complementary and the two straight lines are parallel).

2, when (DC)÷(AB), ∠ 1=∠2, the reason (two straight lines are parallel and the internal dislocation angles are equal). ∠ c+∠ ABC = 180, (two straight lines are parallel and their internal angles are complementary).

When (AD)÷(BC), ∠3=∠C, the reason (two straight lines are parallel and the internal angles are equal).

There is no ∠3 in the picture. I regard the adjacent complementary angle of ∠ADC as ∠3.