The intersection of sets S belonging to A and B is not an empty set. Then, the set S contains at least one of 4, 5 and 6 that satisfies the condition.

Choose one of four, five and six numbers: 3=C3 1.

Two out of four, five, six: 3=C32. Take all four, five and six: 1=C33.

Take a number from 4, 5 and 6, and take one, two and three numbers from 1, 2 and 3: 21= c 31c 31c 32+c 3/kloc 3.

4, 5 and 6 take two numbers, 1, 2 and 3 take one, two and three numbers: 21= c32c31+c32c32+c33c33.

4, 5 and 6 take three numbers, 1, 2 and 3 take one, two and three numbers: 7=C33C3 1+C33C32+C33C33.

Add up the above data. Get 56, and choose B for this question.