Which statement describes a transitional expression for time?

The statement that describes a transitional expression for time is one that indicates a specific relationship regarding when something occurs in relation to other events. "Until then" serves as a clear marker in time, suggesting a point leading up to a specific moment or event. This phrase helps to establish a chronological sequence, making it evident that there is a time frame that needs to be acknowledged before transitioning to another event or situation.

In contrast, the other choices do not serve this temporal purpose. "In addition to" focuses on adding information rather than establishing a time sequence. "Ultimately" suggests a conclusion or final outcome rather than a specific time reference, while "Meanwhile" indicates simultaneous events rather than establishing a clear order of events over time. Therefore, "Until then" is the most appropriate choice for representing a transitional expression specifically related to time.