Which of the following is NOT a characteristic of FIR filters?

A) They can have linear phase response.

B) They require feedback for operation.

C) They are always stable.

D) They can be designed to approximate any desired frequency response.

Answer: B) They require feedback for operation.

Explanation: FIR filters do not require feedback; they only use current and past input values to compute the output. This distinguishes them from IIR filters, which do involve feedback.