客运专线及时速200km/h客货共线Ⅰ级铁路,路堤边坡高度在膨胀土、湿陷性黄土等特殊岩土及岩溶发育区等不良地质区段不应超过()m。
A、8
B、10
C、12
D、15
参考答案:A
— Did you tidy your room?
— No, I was going to tidy my room but I _____ visitors. [ ]
A. had
B. have
C. have had
D. will have
请简述先进控制的概念。