Answer:
b
Step-by-step explanation:
b is undefined bc remember that slope is rise/run
if the "run" is 0, then that makes it rise/0 and dividing by 0 is undefined
a has a positive slope bc it goes up from left to right
c has a negative slope bc it goes down left to right
d has a slope of zero -- and it makes sense bc the rise=0 and dividing zero by a nonzero number will equal zero
