question: What does this type of elevator use to propel the cage ?
answer: a vacuum on top of the cab and a valve on the top of the `` shaft ''
turker_answer: A vacuum on top of the cab and a valve on the top of the `` shaft '' is what this type of elevator uses to propel the cage .
rule-based: A vacuum on top of the cab and a valve on the top of the `` shaft does this type of elevator use to propel the cage .