💡 Detailed Explanation
The verb '思いつく' (omoitsuku) means 'to think of', 'to hit upon (an idea)', or 'to come up with'. It refers to a sudden inspiration or flash of thought entering one's mind. The correct and natural sentence is '良いアイデアを思いついた' (I came up with a good idea). The other options should use verbs like '思い出す' (to recall/remember) instead.