The author states that the research described in the first paragraph was undertaken in order to:
test the hypothesis that meteor streams become broader as they age
This question asks what the author says about the purpose of the research described in the first paragraph.
Testing the hypothesis that meteor streams become broader as they age is the most appropriate answer. According to the author, the purpose of the computer-modeling experiment was to test the hypothesis that meteor streams broaden with time.
Determining the age of an actual meteor stream is not correct; although the observational data described in the last paragraph allowed scientists to estimate the age of the Geminid stream, this data was analyzed to confirm a surprising prediction made by the computer model. This analysis was not part of the original experiment.
Identifying the various features of structural meteor streams is also incorrect. Although the experiment yielded a surprising prediction about a particular feature of meteor streams, the purpose of the experiment was to determine whether meteor streams broaden with time, not to identify the various structural features of meteor streams.
Exploring the nature of a particularly interesting meteor streams is not correct because the experiment was undertaken to test a general hypothesis about meteor streams. It was not undertaken to explore the nature of any particular meteor stream, and the passage never suggests that the actual meteor streams used in the computer model was "particularly interesting."
Showing that a computer model could help in explaining actual astronomical data is not correct. Although the computer model did confirm the astronomers' hypothesis, the purpose of the experiment was not to show that such models are useful.