Chang, R., & Goldsby, K. A.(2013). Chemistry (11th ed.). New York: McGraw Hill.

Cutnell, J. D., & Johnson, K. W.(2013). Introduction to physics (9th ed.). Singapore: John Wiley & Sons (Asia).

Hewitt, P. G., Suchocki, J. A., & Hewitt, L. A.(2010). Conceptual physical science exploration (2nd ed.). California: Pearson Addsion-Wesley.

Hubbart, J. (2011). Hydrologic cycle. Retrieved from http://www.eoearth.org/view/article/51cbee0d7896bb431f695c5e

International Energy Agency (IEA). (2014). Key world energy statistics. Paris: International Energy Agency

Resolution B5 definition of a planet in the solar system. Retrieved from https://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf

Tillery, B. W.(2014). Physical science (10th ed). New York: McGraw-Hill.

Twindell, J. & Wein, T. (2006). Renewable energy resources. New York: Taylor & Francis.