Consider the two statements:
Statement 1: The points A, B, and C will lie on a straight line if ∠ABD + ∠CBD = 180∘.
Statement 2: The angle on a straight line is 180∘.
Both the statements are true and statement 2 is the correct explanation of statement 1
The angle on a straight line is 180∘. Hence, any number of adjacent angles on a straight line add up to 180∘. Conversely, if adjacent angles add up to 180∘ then the angles have to be on a straight line. Hence, A, B and C lie on a straight line. Therefore, both the statements are true and statement 2 is the correct explanation of statement 1