The correct answer is B, which uses a selection edge to specify task behavior based on task priority. In UML, an object flow with a selection property is used to select objects from a collection according to some criterion, which is typically represented by a Boolean expression. In the case of B, the selection criterion is described as
"ordering = the most important first", indicating that tasks are selected to be executed based on their priority.
References:
* UML 2.5 Specification: The UML 2.5 specification describes how selection behaviors can be applied to object flows to filter objects according to specific criteria, such as priority in this scenario.