Analysis: the base of parallelogram is the diameter of semicircle, and the height is the radius of semicircle, that is to say, 2× radius× radius =24, then radius× radius = 24/2 =12; The area of shadow a = the area of trapezoid-half the area of semicircle; B Shadow area = half the area of a semicircle-the area of a right triangle.

Solution: radius × radius =24/2= 12 cm2.

Trapezoidal area: (radius +2× radius )× radius ÷2=( 1+2)× radius× radius ÷2=3× 12÷2= 18 cm2;

Half area of the semicircle: 3. 14× radius× radius ÷ 2 ÷ 2 = 3.14×12 ÷ 2 = 9.42 square centimeters.

Area of a blank triangle: radius × radius ÷2= 12÷2=6 cm2.

Nail shadow area:18-9.42 = 8.58cm2.

B Shadow area: 9.42-6 = 3.42cm2..

Therefore, the area of shadow A is larger than that of shadow B: 8.58-3.42=5. 16 cm2.