A cross section of a developing spinal cord in a vertebrate embryo is shown in the schematic drawing below. Indicate which feature in the drawing (labeled A to E) better matches each of the following descriptions. Your answer would be a four-letter string composed of letters A to E only, e.g. AAEB.

( ) It contains motor neurons.
( ) It is the floor plate.
( ) It secretes BMP and Wnt signals.
( ) It contains sensory neurons.