Question: You need to complete this sentence by selecting always sometimes or never interior angles on the same side of a transversal , cutting parallel lines are length and ruin

1. The problem asks to complete the sentence about interior angles on the same side of a transversal cutting parallel lines. 2. Recall the rule: When a transversal cuts two parallel lines, the interior angles on the same side of the transversal are supplementary. 3. This means their measures add up to 180 degrees. 4. Therefore, the interior angles on the same side of a transversal cutting parallel lines are \textbf{always} supplementary. 5. So, the correct completion is: "Interior angles on the same side of a transversal cutting parallel lines are \textbf{always} supplementary."