Slack workflows can begin from multiple types of triggers rather than being limited to scheduled execution. Workflow Builder supports event-driven automation, and available triggers can include Slack activity, user-invoked links or shortcuts, scheduled execution, webhook-based initiation, and other supported events. Slack's developer examples specifically demonstrate workflows starting when an emoji reaction is applied, while Workflow Builder documentation describes combining supported triggers with workflow steps to create automations. The precise trigger choices available can vary by workflow architecture, workspace plan, and evolving Workflow Builder capabilities, but the central concept remains that workflows can start from many different events or user actions. Therefore, options A, C, and D are overly restrictive. Among the supplied answers, B best represents Slack's event-driven and scheduled workflow-trigger model and is the correct answer.