What is wrong about the synthesis and assembly of collagen?

A、The process of collagen synthesis in cells is：mRNA→precursor chain + propeptide→pro-α chain→procollagen.;

B、Propeptide is a unique sequence of C-terminal and N-terminal of precollagen molecules;

C、The amino acid sequence of TypeⅠ, Ⅱ, Ⅲ collagen polypeptide is arranged as Gly-X-Y tripeptide repeat.;

D、Collagen molecules accumulate directly into collagen fibers through extracellular processing.