The correct answer is Option B based on its visual representation and alignment with the given scenario:
* Class Start Condition: Both diagrams (Option B and Option C) include a decision diamond labeled "10 Students Present?". This captures the condition for the class to start.
* Professor Arrival: Option B explicitly shows the arrival of the professor using an action rectangle labeled "Professor Arrives". This directly addresses the second part of the scenario where the professor's presence is required.
* Start Activity: Both Option B and C have a subsequent activity labeled "Start Class".
Why Option B is More Accurate:
While both Option B and Option C depict the 10 student condition, Option B goes a step further by including the professor's arrival as a separate action, making it a more precise representation of the two-part requirement for the class to start.
Other Options Analysis:
* Option A: This diagram lacks the "10 Students Present?" condition and the professor's arrival, making it unsuitable for the given scenario.
* Option D: This diagram entirely misses the concept of students or the professor, focusing on a different situation.
References
* UML 2.5.1 Specification (Superstructure): Sections on Activity Diagrams, Decisions, and Actions https://www.omg.org/spec/UML/2.5.1/