In view of problems of poor support effect. slow support speed. high support cost and great labor intensity of advance support with advanced hydraulic support. single hydraulic prop or timber in return airway of fully-mechanized high cutting coal mining face of a coal mine in Yulin mining area. https://zbuugh26awr9.timeblog.net/70682638/a-study-of-learners-intuitions-behind-the-use-of-utterance-verbs-in-english