Directions: In the following passage, some words have been deleted. Fill in the blanks with the help of the alternatives given. Select the most appropriate option for each blank.

Water is essential for life, on Earth and other planets but Mars __(1)___ no liquid water on its surface today. The study (Proceedings of the National Academy of Sciences) used stable isotopes of the element potassium to __(2)___ the presence, distribution, and abundance of __(3)___ elements on different planetary bodies. Potassium is a moderately volatile element, ___(4)___ scientists decided to use it as a tracer for more volatile compounds, such as ___(5)__.