Answer:
A. ST = RU
Step-by-step explanation:
Quadrilaterals are four sided figures. Examples are: square, rectangle, trapezium, parallelogram etc. A parallelogram is a quadrilateral that has equal opposite and parallel sides.
This implies that in the given question since RS || TU, then;
RS = TU = 6
So that for RSTU to be a parallelogram,
ST = RU
Thus, the appropriate option to the question is A.