Cellulose, the most important constituent of plant cell wall is made of
(a) unbranched chain of glucose molecules linked by α 1, 4 glycosidic bond
(b) branched chain of glucose molecules linked by β 1, 4 glycosidic bond in straight chain and α 1, 6 -glycosidic bond at the site of branching
(c) unbranched chain of glucose molecules linked by β 1, 4 glycosidic bond
(d) branched chain of glucose molecules linked by α 1, 6 glycosidic bond at the site of branching