题型:填空题 His songs are very _______ and many students like them. [ ]A. good. B. beautiful C. popular D. nice 查看答案
题型:填空题 CY5型操动机构在合闸位置时()原因使油泵启动频繁。A.二级阀的上阀口关闭不严B.分、合闸一级阀口关闭不严C.液压油不清洁,纤维杂质卡入阀口D.安全阀关闭不严,且阀芯与阀体之间结合面处密封不良E.二级阀下阀体与油管结合面渗油 查看答案