1. You should do it yourself.

2. You should do it itself.

Are both grammatical?

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3. She must be angry because she's not saying anything.

4. She has to be angry because she's not saying anything.

Are both grammatical and commonly used?

1 is fine, but 2 doesn't make sense.

3 and 4 are pretty much the same.

Thank you for your help.

5. He hit the boy himself.
6. You should eat the apple itself.

Are the sentences grammatical?

7. I like the boy themselves.

What about this sentence?

5 means that the subject hit the boy; no one else hit the boy.

6 doesn't make sense; remove "itself."

7 doesn't make sense either; remove "themselves."

1. The sentence "You should do it yourself" is grammatically correct. This sentence implies that the person being addressed should personally perform the task instead of relying on someone else to do it.

To determine if a sentence is grammatically correct, you can observe the sentence structure, subject-verb agreement, and usage of appropriate grammar rules. In this case, "You" is the subject, "should do" is the verb phrase, and "it yourself" specifies who should perform the action. The sentence follows standard English grammar rules.

2. The sentence "You should do it itself" is grammatically incorrect. The word "itself" functions as a reflexive pronoun, referring back to the subject of the sentence. However, in this case, "itself" is referring to an inanimate object ("it"), which is not applicable.

To determine if a sentence is grammatically correct, it's important to consider the role and usage of each word within the sentence while ensuring they make sense in the given context.

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3. The sentence "She must be angry because she's not saying anything" is grammatically correct and commonly used. It suggests that the person being referred to is likely angry because of their silence.

4. The sentence "She has to be angry because she's not saying anything" is also grammatically correct and commonly used. It conveys a similar meaning to the previous sentence, implying that the person's silence indicates their anger.

Both sentences are grammatically correct as they follow standard English grammar rules, including subject-verb agreement and proper usage of relevant phrases and conjunctions.

To determine the grammaticality of a sentence, you can check if it adheres to grammatical structures, accurately expresses the desired meaning, and uses appropriate vocabulary and grammar rules for the given context.