第4题: [单项选择]右心衰竭时呼吸困难的机制，主要为 A. 迷走神经兴奋性增高 B. 心肌供血减少 C. 右心房及上腔静脉压力升高 D. 下肢静脉回流增多 E. 肺淤血 参考答案:C
第5题: [单项选择]The government official can hardly find sufficient grounds ______ his arguments in favor of the revision of the tax law. A. on which to base B. which to be based on C. to base on which D. on which to be based 参考答案:A 答案解析:[考点] 考查定语从句。 base…on…意为“把…建立在…的基础上”。which在句中引导定语从句，指代grounds，介词需要置于关系代词之前，故选A。
