The answers are A and D.
The numbers that you cannot simplify without having a radical in the answer are irrational numbers.
√(4/16) = 1/4 or -1/4, rational number
√(9/16) = 3/4 or -3/4, rational number
√(9/4) = 3/2 or -3/2, rational number
√(3/16) = √(3)/4, NOT a rational number, cannot remove radical
√(3/4) = √(3)/2, NOT a rational number, cannot remove radical
