Directions: In the following question, a sentence is given with an underlined phrase. Choose the option that correctly replaces the underlined phrase to make the sentence grammatically and contextually correct. If the sentence is already correct, select "No replacement required".

They shouldn't blames themselves for the accident.

The correct option is shouldn't blame themselves.

Step-by-Step Explanation:

1. Modal Verb Rule:
Modal auxiliary verbs such as should, could, would, can, must, etc. (and their negative forms like shouldn't) are always followed by the base form (bare infinitive) of the main verb, without adding suffixes such as "-s", "-es", "-ed", or "-ing".
In the given sentence, "blames" is in the third-person singular present form. Using "blames" after "shouldn't" is grammatically incorrect. The base form blame must be used instead.

2. Reflexive Pronoun Agreement:
The subject of the sentence is the plural pronoun "They". The corresponding reflexive pronoun used to refer back to a plural subject must also be plural: themselves.

3. Analysis of the Options:
• No replacement required: Incorrect because "blames" incorrectly adds an "-s" after the modal verb "shouldn't".
• shouldn't blame themself: Incorrect because "themself" is singular and does not match the plural subject "They".
• shouldn't blamed themselves: Incorrect because "blamed" is the past tense form, whereas the base form "blame" is required after "shouldn't".
• should not blames themselves: Incorrect because "blames" is used instead of the base verb "blame".
• shouldn't blame themselves: Correct because it properly combines the base verb "blame" with the modal verb "shouldn't" and uses the plural reflexive pronoun "themselves".

Corrected Sentence:
"They shouldn't blame themselves for the accident."