18.99 Connecting the midpoints of the sides of a quadrilateral, the resulting quadrilateral is a rhombus. Then the shape of the original quadrilateral is
(A) Isosceles trapezoid.
(B) Rectangle.
(C) Rhombus.
(D) None of the above conclusions is correct.
(China Guangzhou, Wuhan, Fuzhou and other five cities junior high school mathematics league, 1987)