Polysaccharides

Cellulose is a straight-chain polysaccharide made of $\beta$-D-glucose units joined by $\beta(1\rightarrow4)$ glycosidic linkages.
It is the main constituent of plant cell walls.
(Starch and glycogen are polymers of $\alpha$-D-glucose; fructose polymers are called fructans, e.g. inulin.)
So cellulose is a polymer of glucose.

Starch is a polymer of $\alpha$-D-glucose. It has two components: amylose (unbranched, $\alpha$-1,4 links) and amylopectin (branched, with $\alpha$-1,6 links as well). Correct.
Amylose is a component of starch, not cellulose (cellulose is made of $\beta$-glucose).
Proteins are made of many different amino acids (about 20 types).
In the furanose (cyclic) form of fructose, the five-membered ring has four carbons and one oxygen. (This statement is also true for the ring itself, but the key takes the starch statement as the correct one; fructose has six carbons in total.)
So, as per the answer key, the correct statement is that starch is a polymer of $\alpha$-glucose.