Final answer:
The activities of Tom and Greta since they last met cannot be determined without context; options include traveling, studying, working, or unknown, but specific information is needed to provide a correct answer.
Step-by-step explanation:
Without additional context, it is impossible to answer what Tom and Greta have been doing since they last met. The options provided traveling, studying, working, or unknown are all plausible activities, but without specific information about the story or situation involving these characters, one cannot determine the correct answer. In literature and English studies, understanding character actions and developments often requires attention to detail and analysis of the text provided.