1. Complete the sentences by using the words in the parenthesis.

2. Complete the sentences by using the words in the parentheses.
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Which one is right? Do we have to use the singular form or the plural form at the end of each sentence?

If there is more than one set of words in parentheses, use the plural.

Both sentences are correct, but they have slightly different meanings.

Sentence 1: "Complete the sentences by using the words in the parenthesis."
In this sentence, "parenthesis" is used in the singular form, referring to the singular pair of parentheses.

Sentence 2: "Complete the sentences by using the words in the parentheses."
In this sentence, "parentheses" is used in the plural form, referring to multiple pairs of parentheses.

So, if you use the singular form "parenthesis," it implies that each sentence has only one pair of parentheses. If you use the plural form "parentheses," it implies that each sentence has multiple pairs of parentheses.

The choice between using the singular or plural form depends on the specific context and the intended meaning of the sentence.

Both sentences are grammatically correct, but they have slightly different meanings.

1. "Complete the sentences by using the words in the parenthesis." This sentence is inviting the reader to complete the sentences using the specific words listed within the parentheses.

2. "Complete the sentences by using the words in the parentheses." This sentence is inviting the reader to complete the sentences using any words that fit the general category or theme represented by the parentheses.

Therefore, the choice between singular or plural form depends on the specific context and intention of the sentence.