What is a characteristic of a closed abutment?

Answer: C — It retains the full height of the approach embankment

A closed abutment is specifically designed to retain the full height of the approach embankment, which means it creates a continuous vertical structure that can support the bridge deck while holding back the soil behind it. This type of abutment is integral in maintaining the height and stability of the roadway leading up to the bridge, ensuring that vehicles can safely transition from the embankment to the bridge structure without any abrupt changes in elevation. The other options do not capture the primary function of a closed abutment. While it may have implications for construction time, the ability to retain the approach embankment is the defining characteristic of closed abutments. Additionally, they typically do not allow for a very low span length; that characteristic is more related to the design and requirements of the bridge than to the nature of the abutment itself. Furthermore, the presence of wing walls is not a characteristic of closed abutments, which differentiates them from other types that may include extensions to aid in soil retention and drainage.