Which Structural Property Is Common Among Glutamate Receptors and K_CS

Which structural property is common among glutamate receptors and K_CS potassium channels?

A) Ion selectivity of the pore
B) The number of transmembrane segments that comprise the receptor/channel
C) A small helical region between transmembrane segments that forms the pore
D) Positively charged amino acids located at every third position in one of the transmembrane domains
E) The pore region located on the cytoplasmic side of the receptor/channel