The sequence diagram given in Figure 1 for the Weather Information System takes place when an external system requests the summarized data from the weather station. The increasing order of lifeline for the objects in the system are:

1. ASatComms → Weather station → Commslink → Weather data
2. BSatComms → Commslink → Weather station → Weather data
3. CWeather data → Commslink → Weather station → SatComms
4. DWeather data → Weather station → Commslink → SatComms

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Correct answer: C. Weather data → Commslink → Weather station → SatComms

Explanation

In the diagram, Weather data is active only for the summarize call, Commslink a little longer, Weather station longer still, and SatComms spans the whole exchange.