ANS:B - clampers

"clamper" as an answer for this question is very awkward. A circuit that alters the DC level of an arbitrary signal is most commonly labeled "level shifter". "Clamper" is more associated with a circuit whose output generally is ideally a linear representation of an input signal till the output reaches a level beyond which the circuit will produce no more output current and/or voltage.

At the point of "clamping" the circuit is non-linear. All amplifiers will naturally "clamp" depending on supply voltage magnitude or maximum output current limits; amplifiers can be designed to clamp at arbitrary voltage or current outputs.