Rotating CD 180 degrees around the point D would mean rotating it to the other side of D, in other words, rotating it clockwise. The new line would be D->M->C
Rotating CD 180 degrees around the point E would mean rotating it clockwise till "E" is a point of the line. The new line would be E->M->D.
Rotating CD 180 degrees would keep the line in the same position right now but with CD being in different order. The new line would be D->M->C.
Best of Luck!
