Which sentence uses a transition word or phrase to signal a shift in time?

A.
In the apartment across town, George sat down at his computer.
B.
After a few hours of work, he was finished with his masterpiece.
C.
Meanwhile, his editor in New York City could hardly wait to read the finished product.
D.
George had spent nearly a year working on this novel about the old West and the surly outlaw who loved it.