So let's assume that Door A is Sports car. Door B and C are toy.

At first time, if you chose door A, and if you switch afterward, you will 100% get toy.

At first time, if you chose door B, and if you switch afterward, you will 100% get sports car.

The same with C, at first time, if you chose door C, and if you switch afterward, you will 100% get sports car.

Therefore if you switch afterward, the probability of getting sports car is $$\frac{2}{3}$$.

If you don't understand, I can explain further.