YOU SAID:

My sister is in eighth grade and is passing to the ninth grade

INTO JAPANESE

私の妹は中学2年生で、中学3年生になります。

BACK INTO ENGLISH

My sister is in the second year of junior high school and is in the third year of junior high school.

INTO JAPANESE

姉は中学２年生、中学３年生です。

BACK INTO ENGLISH

My sister is in the second year of junior high school and the third year of junior high school.

INTO JAPANESE

姉は中学２年生と中学３年生です。

BACK INTO ENGLISH

My sister is in the second year of junior high school and the third year of junior high school.