Answer: Hello mate!
the phrase is:
"In a plane, if one of two parallel lines is _____ to another line, the other of the two lines is perpendicular to that line."
the angle between two parallel lines is equal to zero.
if one of the parallel lines is perpendicular to a third line, this means that the angle formed by bot lines is equal to 90°.
And because the second parallel line has an angle of 0° with respect of the first one, then the angle formed with the third line is also 0° + 90° = 90°, so is also perpendicular.
Then the answer is "perpendicular".
