As I receive your submissions for the chapter 9 survey, I see that we need to pay closer attention to whether the sentence is in the present or past. "They GO UP on the chairlift" is present tense. "They WENT UP on the chairlift" is past tense. SUBIR is an -IR verb so, in the present tense, the sentence would be "Ellos SUBEN por el telesilla." In the preterit tense, the sentence would be "Ellos SUBIERON por el telesilla." Since we have only learned the preterit tense of the AR verbs, you won't be expected to put SUBIR in the past tense on this test! However, still be watching for present vs past tense!