Questions & Answers about gonghangi neomu keoyo.
크다 (to be big) is a 2nd-class adjective whose stem ends in ㅡ. When you add -아/어요, you drop the ㅡ and attach -어 (because the other vowel in the stem isn’t ㅏ or ㅗ), then -요. So:
• 크다 – stem: 크
• 크 + 어요 → 커요