Chất nào sau đây là đipeptit? H2N-CH2-CO-NH-CH2-CH2-CO-NH

H2N-CH2-CO-NH-CH2-CH2-CO-NH-CH2-COOH.

H2N-CH2-CO-NH-CH(CH3)-CO-NH-CH2-COOH.

H2N-CH2-CO-NH-CH2-CH2-COOH.

H2N-CH2-CO-NH-CH(CH3)-COOH.