Let S be the set of the 50 United States. Which of these four binary relations on E isnotan equivalence relation?

(For the purposes of this question, "vowel" means "A, E, I, O, or U"}

Select one:

a. E = {(x, y): x and y contain exactly the same set of vowel in their names}b. E = {(x, y): the names of x and y have a vowel in common}c. E = {(x, y): if we delete all the non-vowels from the names of x and y, the same string remains}d. E = {(x, y): Every vowel in x's name also occurs in y's name, exactly the same number of times}