Group the following words into denominal nouns, deverbal nouns and de-adjectival nouns, according to the noun suffixes fixed at the end of each word.
cigarette，slavery, productivity，protection, assistant，trainee, largeness，friendship
【正确答案】：Denominal nouns: cigarette, slavery, friendship
Deverbal nouns: trainee, assistant, protection
De-adjectival nouns: productivity, largeness
