Recall the structure of maltose

Maltose is a disaccharide formed by two glucose units joined through an $\alpha(1\to 4)$ glycosidic bond.

So, one glucose unit uses its anomeric carbon to form the glycosidic linkage, while the other glucose unit still has a free anomeric carbon.

Identify the functional group at the glycosidic carbon

In cyclic sugars:

• A carbon attached to two alkoxy groups $( -OR )$ is an acetal (if derived from an aldehyde).
• A carbon attached to one alkoxy and one hydroxyl is a hemiacetal.

Since glucose is an aldose, its cyclic form gives hemiacetal/acetal terminology, not hemiketal/ketal.

Apply this to maltose

• The first glucose unit has its anomeric carbon involved in the glycosidic bond. Hence that carbon becomes an acetal.
• The second glucose unit has a free anomeric carbon. Hence that carbon remains a hemiacetal.

Check the options

• A: One acetal and one ketal $\rightarrow$ incorrect, because glucose is an aldose, not a ketose.
• B: One ketal and one hemiketal $\rightarrow$ incorrect for the same reason.
• C: Two acetals $\rightarrow$ incorrect, because one anomeric carbon is still free.
• D: One acetal and one hemiacetal $\rightarrow$ correct.

Final answer

Maltose contains: $\boxed{\text{One acetal and one hemiacetal}}$