Which of the following is correct structure of -anomer of maltose?

Step 1: Maltose Composition — Maltose is a disaccharide made of two glucose units connected by an $\alpha\text{-1,4-glycosidic}$ bond.

Step 2: Anomeric Carbon State — The $\alpha$-anomer of maltose refers to the free hemiacetal carbon (C1 of the second glucose unit) being in the $\alpha$-position (OH pointing down in the Haworth projection).

Step 3: Identification — Analyzing the provided structures, (d) shows the correct $\alpha\text{-1,4}$ linkage between two glucose units and the correct $\alpha$-configuration at the reducing end.

Key Point: Maltose exists in equilibrium between $\alpha$ and $\beta$ forms in solution due to mutarotation at the free hemiacetal carbon.