A) is correct because squares and parallelograms are all four sided, which make them quadrilaterals.
B) is correct because both opposite sides of squares and parallelograms are parallel.
C) is correct because the two sides that are sandwiching the non-parallel sides are parallel.
Q3: The figure is a trapezium, because the parallel sides of a trapezium are of the same length, and the pair of opposite angle both add up to 180º.
Q4: I do not agree with the statement, because parallelograms' two opposite sides are of the same length, but ALL sides cannot be of the same length.