In order for a relation to be a function, each input (x) must have a unique output (y). A vertical line test can be used when a graph is presented to see if the relation is a function; if a vertical line is dropped through the function and passes through more than one point, the relation is NOT a function.
For this problem, A and E are NOT functions. In example A, the letter C maps to two different values, and in example E, when a vertical line is dropped through the function, the line passes through more than one point.
Therefore, the functions are B, C, and D,