老年男性泌尿系梗阻常见原因
A．结石，损伤，肿瘤或结核B．盆腔内疾病C．先天性畸形D．前列腺增生症E．包皮过长
参考答案：D
化学就在我们身边． 现有下列四种物质；尿素、石油、汞、合成橡胶、请选择相应的物质填空：①可做汽车轮胎的材料是______ ②温度计中填充的液态金属是______
③可作氮肥的是______ ④被称为“工业的血液”的化石燃料是______．
Monopolists will maximize profit by producing at an output level where which of the following conditions exists（）
A. Price = marginal revenue = marginal cost.
B. Price = demand = marginal revenue = marginal cost.
C. Marginal revenue = marginal cost ＜ price.
