Why is that a question can be answered with several theories? This may be silly and I am sorry for that but it is confusing me. My teacher was teaching us about path of electrons around a nucleus. He told us that many theories have been proposed about path of an electron and the latest theory is somehow different from saying that electron revolves in a circular path around nucleus. Even though he used the circular-path theory (temporarily called so) to demonstrate other phenomenons such as Ionization Potential, vaporization etc and it all seems logical. He also said that other theories concerning to electronic path can also be used to demonstrate these phenomenons but I am using this since this is simpler. 
But how this is possible? I am thinking that these things must be working under a single theory (may be one among them or one uncovered so far) naturally then why a question can be answered with several theories completely logically.
 A: A "theory" is nothing more than a recipe to describe a natural phenomenon.
There can be many theories to describe the same thing, just as I can use different words to describe the same object.
Theories can be very different from one another for several reasons.
They can describe the same exact phenomenology with different formalism (different words for the same object), or can describe different aspect of that phenomenon (using more words to better describe the characteristics of the object).
A: Because a theory only covers what is known at the moment. In the future new features and behaviour may be discovered to apply in certain situations. A new theory must then be made that covers the old theory AND the new discoveries and takes it all into account. 
For example, the original Bohr model of the atom as electrons in circular orbits orbiting the nucelus appears to lack certain details in certain situations and had some flaws in expaining certain things. So the quantum theory has arrived to explain that. Therefore the Bohr model is not accurate in all areas. Even so it is still used.
Why? Because it is still usable within a certain scale (where quantum effects are so tiny that they are negligible). So we can use a theory or model as long as we know the range of application of it. Within the range, it may be utilized, and outside of the range we must remind ourselves that now the previously insignificant behaviours are not insignificant anymore, and another model (if it has been made) must be used instead at this scale.
