Why is it incorrect to classify the polygon shown as a parallelogram?

A. It has four sides.
B. Some sides are shorter than others.
C. It has only one pair of parallel sides.
D. All the interior angles have different measures.

Which of these is a disadvantage of hydrogen fuel cells? a. engines that use hydrogen fuel are more efficient than gasoline-powered engines. b. the only emission produced by hydrogen fuel cells is water. c. hydrogen fuel is continually available and useful for heating. d. hydrogen fuel is often purified in a process that emits lots of greenhouse gases.