A deck, unlike a balcony, _____________________ constructed as a free-standing feature of a house.

In the context of home construction and architecture, the distinction between a deck and a balcony lies in their structural characteristics and how they are integrated into a building. A deck is typically an outdoor feature that can exist independently and is often built as a free-standing structure, meaning it does not have to be directly attached to the house itself. This allows for greater flexibility in design and placement.

Choosing "can be" indicates that a deck has the option to be constructed as a free-standing feature, highlighting its versatility. This term encapsulates the possibility without imposing a requirement.

In contrast, terms like "must be" or "is" suggest a more definitive condition which is not accurate for decks, as not all decks are required to be free-standing—they can also be attached to structures. "Should be" implies a recommendation rather than an option or ability, which also does not capture the nature of decks fully.

Therefore, the use of "can be" correctly reflects the characteristic flexibility in the construction of decks compared to balconies, making it the right choice for the question.