My car is good.
My car is better than my sister's car.
My car is best among all the cars.

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1.
Anna: my car is good then the sistr car
Correct: My car is good.
Explanation:
*Begin the sentence with a capital letter and end it with a period.

2.
Anna: my car is better
Correct: My car is better than my sister's car.
Explanation:
*Begin the sentence with a capital letter and end it with a period.
*Use better than to compare two things.
*To show possession, add an apostrophe and letter s ('s)

3.
Anna: my car is best
Correct: My car is best among all the cars.
Explanation:
*Begin the sentence with a capital letter and end it with a period.
*Use best to compare one thing with the others.

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Hello, Anna! Thank you for submitting your homework. Please read the following corrections and explanations carefully. If you have questions and clarifications, you can ask me in our class. Thank you!