Period subdivisions

Exercise 17

Assign/devise subject headings for the following topics:

a. A history of the West Indies focussing on the 18th century:
West Indies - History - 18th century

b. Economic conditions in Queensland in the 21st century:
Queensland - Economic conditions - 21st century

c. Social conditions in the United States of America in the 1950s and 1960s:
United States - Social conditions - 20th century (this is because it says in SCISSHL: "Indexing Note: May be subdivided like Australia except for the period subdivisions of history", otherwise it would read: United States - Social conditions - 1950-1970.) (No, apparently I missed something, because the answer reads: United States - Social conditions - 1945-1974... Ah-ha! I get it. When you searh for "United States" in SCISSHL, it lists all the options for subdivision of that term, including all the history ones. The time frames are already chosen for us - we can't choose them ourselves - that is what the indexing note was referring to I think...)
So, United States - Social conditions - 1945-1974.