On a coordinate plane, line A has a negative slope, line b is horizontal, line c is vertical, and line d has a positive slope.
Which line has a slope of zero?
Line a
Line b
Line c
Line d

Answer asap and if you do you will get brainliest. catherine buys a gallon of ice cream from the store. after taking it home, she eats a fifth of a gallon of ice cream. her sister eats some of the ice cream as well. if two-thirds of the original amount of ice cream is left, then what fraction of a gallon of ice cream did her sister eat?