A probability game of "3 to 1" is a bit test of intelligence

Game: There are three doors, namely car and sheep. Only one door is car. Assume that a door is selected immediately. If a car is behind the door, you can get the car. Otherwise, you will get the sheep. Obviously, we guess the probability of a car is 1/3. But now, the condition is that there is a host who knows what is behind each door. When you choose a door, she opens a door with sheep. Do you want to change your original choice? Stick to the original choice, and change the probability of the original choice.

Please give an explanation.

The answer is 1/3 to 2/3. Probability can be explained, and programming is more intuitive.