Answer: a. use of liquid fuels
The space exploration is a wide field that deals with the study of celestial bodies such as stars, planets and the entire solar system. The study involves the use of the telescopes, robotic space probes and human spaceflight using special spacecrafts. The use of the liquid fuels can aid in the movement of the spacecraft or satellite which can help in the exploration of space, this can bring some relevant information about the various bodies of the space and related to the physical environment of the space. This will help in direct exploration of the space.
