Sentence:  To prevent the manager from deliberately controlling himself only during the sessions , they were rather lengthy ( about <WSD>twenty</WSD> minutes ) , the situations were imperfectly described to the manager so that he would not know what to expect , new antagonists were brought on the scene unexpectedly , and the antagonists were instructed to deliberately behave in such ways as to upset the manager and get him to operate in a manner for which he had been previously criticized . 
Meaning of the word marked with <WSD> tags:  denoting a quantity consisting of 20 items or units