Why is the expression $12 \div 0$ considered undefined?

Because the related multiplication $0 \times c = 12$ has no solution.

Because the related multiplication $12 \times c = 0$ has one solution.

Because any number multiplied by zero is zero.

Why is the expression $0 \div 0$ considered undefined?

Because its related multiplication equation has no solution.

Because its related multiplication equation is true for every number, so there is no unique answer.

Because the only possible answer is 0.

Because the only possible answer is 1.