Step 1: Recall the vocabulary of sugar isomers. Epimers differ at one carbon that is not C1; enantiomers are non-superimposable mirror images differing at every stereocentre; anomers differ only at the newly formed anomeric carbon after ring closure.
Step 2: The α and β forms of D-glucose are produced when the straight-chain form cyclises; the only stereochemical difference between them is at C1, the hemiacetal (anomeric) carbon. Every other stereocentre stays the same.
Step 3: A difference confined to the anomeric carbon exactly matches the definition of anomers, and their interconversion in solution is mutarotation.
Result: α-D(+)glucose and β-D(+)glucose are anomers, alternative (iv).