Answer:
only A
Explanation:
A is correct because if a number is less than 7, the number under the square root will be negative, and that will yield an imaginary (or non-real number)
B is incorrect because even if you choose a number less than 7, the result will still yield a real number
C is incorrect due to the same logic as B
D is incorrect because you can take the cube root of a negative number without it being non-real.