💡 Detailed Explanation
The correct answer is 資源 (shigen), meaning 'resources' (natural, economic, etc.). The other options are homonyms: 私言 (shigen) means 'personal opinion', 始原 (shigen) means 'origin' or 'beginning', and 至言 (shigen) means 'wise saying' or 'maxim'. The context of 'limited' and 'use carefully' points to 'resources'.