Step 1: In the Haworth projection of D-glucopyranose, the anomeric carbon is $C_1$.

Step 2: In $\alpha$-D-glucose, the –OH on $C_1$ points below the plane of the ring (on the opposite side from the $CH_2OH$ at $C_5$, i.e. trans to it). In $\beta$-D-glucose, this –OH points above the ring (cis to the $CH_2OH$).

Correct option: (a) — the structure with the $C_1$–OH group drawn below the ring plane represents $\alpha$-D-glucose.