Black copper marans - rooster or hen?

[Cygne]

Hi, it's about 4 weeks we are raising baby chickens. We have 5 blue marans and 4 black marans. We are pretty sure about a gender of 8 chicks. But the last one, I don't know. Compared to 3 other black chicks (I think they are rooster) that one doesn't have such big red comb and is pretty docile, but it is the biggest chick. Can you please help me identify gender of this chick? Thank you.

 

[oldhenlikesdogs]

Cockeral