Final answer:
To simplify the given radical expressions, we need to analyze each option and determine if it can be simplified further.
Step-by-step explanation:
To simplify the radical expressions, let's look at each option:
A) √(-9): The square root of a negative number is not defined in real numbers. Therefore, the expression cannot be simplified in real numbers.
B) 3i: This is an imaginary number, which represents the square root of a negative real number. The expression is already simplified.
C) -9: This is a real number, and it is already simplified.
D) 0: The square root of 0 is 0. The expression is already simplified.
Therefore, options B, C, and D are already simplified.