Cost-volume-profit(CVP)analysis is a key factor in many decisions, including choice of product lines, pricing of products, marketing strategy, and use of productive facilities. A calculation used in a CVP analysis is the breakeven point. Once the breakeven point has been reached, operating income will increase by the ( )成本-数量-利润（CVP）分析是许多决策的关键因素，包括产品线的选择、产品的定价、营销策略和生产设施的使用，CVP分析的一个内容是计算盈亏平衡点。一旦达到盈亏平衡点，营业收入将按以下哪项规律增加 ( ) A. Gross margin per unit for each additional unit Sold. 额外售出产品的单位销售毛利。 B. Contribution margin per unit for each additional unit sold.额外售出产品的单位边际贡献。 C. Fixed costs per unit for each additional unit sold. 额外售出产品的单位固定成本。 D. Variable costs per unit for each additional unit sold.额外售出产品的单位变动成本。