A.20

b22

Correct answer: a

What is the minimum recovery step after any third-order Rubik's cube is disrupted? This problem has puzzled mathematicians for more than 30 years, and this minimum step size is also called "magic number". Scientists in California recently solved this mystery with computers. They proved that any combination of the Rubik's Cube (the third-order Rubik's Cube has 43,252,003,274,489,856,000 different possible combination states (about 4.3× 10 to the power of 19) can be restored in 20 steps. Therefore, the number of gods =20.