【正确答案】正确答案：The words "deceased" "upper" and "downer" have undergone a process of class shift. By shifting the word class one can change the meaning of a word from a concrete entity or notion to a process or attribution. This process of word formation is also known as zero-derivation, or conversion. In the sentences above, "deceased" , "upper" and "downer" are originally adjectives, meaning "dead", "higher" and "lower" respectively; in the sentences above, however, they mean " dead people" , "a drug used as a stimulant. " and " a depressant or sedative drug" , which are nouns.