Which sentence is grammatically correct?

The sentence "The students looked at their test scores" is grammatically correct because it uses "their" properly to indicate possession. In this context, "their" refers to the students, showing that the test scores belong to them. This structure follows the standard rules of English grammar, as it clearly conveys the relationship between the subjects (the students) and the object (the test scores) without any errors in word choice or structure.

The other sentences contain various grammatical issues, such as incorrect word usage or punctuation errors, which disrupt the clarity and correctness of their meaning.