If line ab is parallel to line cd, and line cd is perpendicular to line ef. what can you conlude about ab andef

If line AB is parallel to line CD, and line CD is perpendicular to line EF, AB is perpendicular to line EF due to the perpendicular transversal theorem,which says, if a line is perpendicular to another line, then it is perpendicular to the line parallel to the second line.

This theorem can be proved through the transversal postulate and theorems.