Cellulose's linear β-linked structure Steps:

• Identify cellulose as a polymer of β-D-glucose units linked by β-1,4-glycosidic bonds.
• Note these bonds create a straight, unbranched chain unlike α-linked branched polysaccharides.
• Recognize intermolecular hydrogen bonds stabilize parallel chains for rigidity.
• Confirm absence of branches, distinguishing it from glycogen or amylopectin.

Why D is correct:

• D matches cellulose's properties: no α-linkages (x), unbranched chain (✓), no intramolecular H-bonds (x), branches not present.

Why the others are wrong:

• A incorrectly states branched structure and vague "key present" without defining it.
• B wrongly indicates branched chain, which applies to glycogen, not cellulose.
• C mismatches by lacking confirmation (✓) for unbranched structure and H-bond placement.

Final answer: D