Quadrilateral abcd  is a parallelogram. ac=bd  ,ac    bisects bd  , and  .  what is the best  name for quadrilateral abcd? a. rectangle c. isosceles trapezoid b. rhombus d. square      

Rectangle since a trapezoid is not a parallelogram, and since two side are equal.

AC = BD where AC bisects BD which means AC and BD are the diagonals

since both diagonals are equal then, all the sides of the plane must be EQUAL

so it's either rhombus or square

square is a rhombus
but not all rhombus is a square ;)