Based on the diagram shown, all of the following are true statements except

You are correct. The answer is choice C.
The other choices A, B, D have each side add up to 180 degrees either because the angles are a linear pair (adjacent and supplementary) or because the angles are same side interior angles. Same side interior angles are supplementary if a transversal line cuts through a pair of parallel lines as so happens in this diagram.
Answer:
Step-by-step explanation:
We are given a triangle an a parallel line l to thr base of the triangle m.
l || m.
Let us check each statement one by one.
According to first statement
m<1 +m<2 = m<3+m<4
Angle m<1 and m<2 makes a linear pair and sum of linear pair angles is 180°.
Angle m< 3 and m < 4 also make a linear pair.
Therefore, m<1 +m<2 = m<3+m<4 is correct.
Second statement
m<1 +m<5 = m<3+m<4
m<1 and m<5 are Consecutive Interior Angles and sum of Consecutive Interior Angles between two parallel lines is 180°.
Angle m< 3 and m < 4 also make a linear pair. Sum of those angles also 180°.
Therefore, m<1 +m<5 = m<3+m<4 statement is also correct.
Third Statement
It is not given that m<4 = m<6.
Therefore, we can't say m<1 +m<6 = m<4+m<6.
Fourth statement
m< 3 +m<4 = m<7+m<4
Angle m< 3 and m<4 makes a linear pair and sum of linear pair angles is 180°.
m<7 and m<4 are Consecutive Interior Angles and sum of Consecutive Interior Angles between two parallel lines is 180°.
Therefore, m< 3 +m<4 = m<7+m<4 is also true.
Finally we could say that third statement
m<1 +m<6 = m<4+m<6 is not true.