The level 2 vocab item says 山に登り (やまにのぼり), however there is also a level 6 kanji item which instead says 山登り (やまのぼり)...
It is certainly a bit weird. Almost everytime I answer that vocabulary question on here I forget to put the に it wants, but didn't stop to think about the fact the に may well have been put there as a typo. If it were for the verb phrase "climb a mountain", やまにのぼる / やまにのぼります would be fine.
山に登り (やまにのぼり) in and of itself isn't "wrong", but just that it seems a strange choice of translation if it's intended to be the noun for the activity of "moutain climbing".
February 25, 2017 at 5:54am