Which One of the Following Statements Correctly Describes How Stream

Which one of the following statements correctly describes how stream terraces can form?

A) Base level rises; the stream downcuts, and the old floodplain is left well above the elevation of the present- day channel.
B) A temporary base level is eliminated; the stream builds its channel upstream from the old temporary base level, and the former floodplain is left well above the present elevation of the stream.
C) A temporary base level is eliminated; the stream downcuts upstream from the old temporary base level, and the former floodplain is left well above the present elevation of the stream.
D) Base level drops; the stream aggrades its channel, and the former floodplain is left below the present elevation of the stream.