What is the contrapositive of the conditional statement? If two variables are directly proportional, then their graph is a linear function. O If two variables are directly proportional, then their graph is not a linear function. O If two variables are not directly proportional, then their graph is not a linear function. O If the graph of two variables is a linear function, then the two variables are directly proportional. O If the graph of two variables is not a linear function, then the two variables are not directly proportional. ​