Hey there! I'm happy to help!
The slope is the incline of a line, or how steep it is.
If a slope is positive, it is going upwards, and if it is negative, it will be going downwards.
We see that our line is going horizontally, so answers A and D are incorrect as it is not going diagonally upwards or downwards.
If a line is vertical, it has no slope. Since it is only going up and down and not side to side, there is no slope. However, this line is horizontal, so it still has a slope. Answer C is incorrect.
This line has a slope of B) 0. This is because our line is going side to side, but it isn't going up. So, our slope is just flat, or a slope of zero.
Have a wonderful day and keep on learning! :D