Answer:
(D) C'D' and CD are equal in length
Explanation:
When we reflect a line, nothing changes about it except it's position.
The line never gets dilated in any way.
This means that B and C must be incorrect, since they refer to dilating the line.
Now we can think about it. If we reflect a line across the y-axis, that means that the line will be parallel to the original line. This means A is false.
That leaves D.
Hope this helped!