1. I'm in the third year of middle school.
2. I'm in the third year in middle school.
(Which preposition do we have to use?)
3. My school is a boys-only school.
4. My school is a boys' school.
5. My school is girls-only school.
6. My school is a girls' school.
(Are all OK? Which ones are commonly used?)
1 and 2 - Both prepositions are fine in this construction.
3 - 6 - All are OK. 4 and 6 are most commonly used.
1. "I'm in the third year of middle school." - This sentence is grammatically correct and commonly used to indicate that you are currently in your third year of middle school.
2. "I'm in the third year in middle school." - This sentence is incorrect. The correct preposition to use in this case is "of," as in the first sentence.
3. "My school is a boys-only school." - This sentence is grammatically correct and commonly used to indicate that the school only admits boys.
4. "My school is a boys' school." - This sentence is also correct, but it has a slightly different meaning than the previous sentence. It implies that the school is affiliated with or primarily designed for boys, but it may admit female students as well.
5. "My school is girls-only school." - This sentence is incorrect. The correct form would be "My school is a girls-only school," which means that the school only admits girls.
6. "My school is a girls' school." - This sentence is also correct and carries a similar meaning to sentence number 4. It suggests that the school is associated with or mainly intended for girls but may accept male students too.
Overall, sentences 1, 3, 4, and 6 are commonly used and grammatically correct. Sentences 2 and 5 contain errors in terms of preposition usage and should be revised for clarity.