参考文献：
[i] https://www.hdb.gov.sg/cs/infoweb/residential/renting-out-a-flat-bedroom/renting-out-your-flat/eligibility
[ii] https://www.hdb.gov.sg/cs/infoweb/residential/renting-a-flat/renting-from-hdb/public-rental-scheme/rents-and-deposits
[iii] https://dollarsandsense.sg/guide-to-hdb-2-room-short-lease-flexi-flat-for-retirees/
[iv] https://www.hdb.gov.sg/cs/infoweb/residential/renting-a-flat/renting-from-the-open-market/regulations-for-renting-out-your-flat
