Which of the following statements about non-collagen adhesive proteins is wrong? A: The fibronectin mediates cell to cell adhesion. B: The molecular structure of fibronectin exhibits multi- domains for specific function. C: RGD tripeptide is the smallest structural unit of non-collagen binding proteins in ECM for cell to associate. D: Laminin is a hetero-trimmer protein composed of three polypeptide chains of α、β and γ.