I’m stuck on this I don’t understand.

Hello from MrBillDoesMath!
Answer:
The first choice (with the square roots of negative integers)
Discussion:
Number such as 0,1,2,3 or -4, -5, -8, or Pi, sqrt(12), sqrt(15), or 1/2, 1/10, 1/14 are all REAL numbers.
The square root of a negative number, such as sqrt(-3), is an imaginary number. The answer is the first choice
Thank you,
MrB