Incised meanders a. develop when the stream gradient is steepened or discharge decreases. b. form when base level remains stable for long periods of time. c. can result from either superposed or antecedent stream activity. d. are demonstrating a feature of stream immaturity (meanders) in a mature setting (steep walls).

d. are demonstrating a feature of stream immaturity [meanders] in a mature setting [steep walls].

Explanation:

Incised Meander is a river meander which has been cut abnormally into landscape because uplift of land has caused downward erosion by the river. This represents stream immaturity and level of rivers is not stable.