Consider U = {x|x is a negative real number}.Which is an empty set?
A
{x|x ∈ U and x has a negative cube root}B
{x|x ∈ U and x has a negative square root}C
{x|x ∈ U and x is equal to the product of a positive number and –1}D
{x|x ∈ U and x is equal to the sum of one negative and one positive number}