The correct answer is B. Flow Efficiency measures the percentage of time spent on value-added activities in the Value Stream. A Value Stream is a sequence of activities that deliver value to the customer, from concept to cash. Value-added activities are those that directly contribute to the customer value proposition, such as coding, testing, and deploying. Non-value-added activities are those that do not directly contribute to the customer value proposition, such as waiting, handoffs, rework, and approvals. Flow Efficiency is calculated by dividing the total time spent on value-added activities by the total flow time, which is the time elapsed from when a work item enters the Value Stream to when it is delivered to the customer. Flow Efficiency is a metric that helps to identify and eliminate waste and delays in the Value Stream, and to optimize the flow of value to the customer. Flow Efficiency can be improved by applying the principles and practices of DevOps, such as reducing batch size, limiting work in progress, implementing pull systems, managing queue lengths, reducing handoffs, implementing Work in Process (WIP) visualization, and implementing Work in Process (WIP) feedback