💡 Detailed Explanation
'Toboshii' means that something necessary is insufficient or not enough, and is often used for abstract things like knowledge, experience, or resources. 1 is the correct usage, meaning 'lacking in experience.' For 2 and 3, which refer to a small concrete quantity, '少ない' (sukunai - few/little) is more natural. For 4, which refers to a lack of skill, '下手だ' (heta da - unskillful) or '苦手だ' (nigate da - weak at) should be used.