Question

which of the following word is not a compound words for this hardship, innumerable, working-class​

Answer 1

As a general rule, then, the plural form of an element in a hierarchical term belongs to the base element in the term, regardless of the base element's placement:

first sergeants

sergeants major

sergeants first class

colonel generals [Russian]

lieutenant generals

lieutenant colonels

apprentice, journeyman, and master mechanics

deputy librarians

deputy assistant secretaries of state

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