Select all the true statements about relations and functions.
 a All functions are relations, but not all relations are functions.
 b The domain of a function is all the output values.
 c If a relation is a function, each input value will have only one output value.
 d If a relation is not a function, at least one input value will have more than one output 
 value.
 e In a function, the output is the dependent variable and the input is the independent variable.