This paper discusses the sluicing phenomenon in Chinese and proposes that the so-called sluicing with obligatory shi is actually an embedded phrase of an identification sentence with a dropped subject, whereas sluicing with optional shi is said to be true
王成东.汉语中的真假疑问删略句[J].重庆工商大学学报(自然科学版),2007,(7): WANG Cheng-dong. On the True and So-called Sluicing in Chinese[J]. Journal of Chongqing Technology and Business University(Natural Science Edition),2007,(7):