The correct answer is C. In my American history class, we studied the effects of World War I
Explanation:
In general terms, a word is considered as being used correctly in a sentence if the word is used according to the type of word it is such as noun, adjective, verb or adverb and if its meaning fits with the context of the sentence. In the case of the word effect, this word is a noun which means it can be used as a subject or direct object in a sentence and it means a consequence or result of some event or situation.
According to this, the sentence that uses the word effect correctly is "In my American history class, we studied the effects of World War I" because in this sentence the word "effect" is a direct object of the verb "study" which means it remains as a noun and also, the meaning of the word "consequence or result" fits with the context as the effects of World War I refer to the consequences or results of this word. Also, in other sentences, the word "effects" is used as a verb, which is not correct as this is a noun.
