What is the domain of the relation?

{(-4.5, 0),(-3, 9), (0.9, 0),(4, - 7.8),(4, 0), (17, 3)}

a. {0.9, 4, 17}

b. { -4.5, -3, 0.9, 4, 17}

c. {-7.8, 0, 3, 9}

d. {-4.5, -3}