= Solution
A \b[<sequence diagram>] describes an interaction among participants using lifelines and ordered messages; time normally runs downward. Calls, replies, and execution intervals show a scenario such as the client asking a Sports wrapper for its cost, then that wrapper delegating through the inner packages to `BasicPlan` and adding charges on return. Alternatives or loops can describe more than one trace.
A \b[<state diagram>] describes states of an object or system and transitions triggered by events, possibly guarded by conditions and accompanied by actions. An account might move from active to suspended on a failed-payment event and back to active on payment. It describes allowed lifecycle behavior rather than the order of messages in one chosen interaction. Both are behavioral diagrams in <UML>.
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