Topic sentences have a dual purpose to:
a) communicate the purpose of the paragraph and provide exciting details.
b) provide exciting details and relate the paragraph back to the thesis.
c) communicate the purpose of the paragraph and relate the paragraph back to the thesis.

c) Communicate the purpose of the paragraph and relate the paragraph back to the thesis.

Explanation:

Topic sentences are the first sentences that the reader reads when facing a document, so they have to be clear about the purpose of the paragraph and the thesis and reasoning that is going to be exposing, and showing the conection to the main thesis of the document.

well, number 1, the 1920s was not economically prosperous until the start of the lend-lease act, which employed large amounts of people in producing equipment for the allies.

b. world war ii is your answer, because wwi had already ended at 1918, and the cold war was after 1945.

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