The Bose-Einstein condensate is formed by: 

Bose-Einstein Condensation or BEC is a state of matter developed in the 19^th century. In BEC, the atoms as a whole behave like a single quantum entity. The atoms do not have a movement relative to each other. The state BEC is achieved by cooling down a very low dense gas to very low temperature. 

Solid, liquid, gaseous, and plasma are the four commonly understood states of matter. Around 1990, the Bose-Einstein condensate state of matter was developed. It is a collection of atoms that, when chilled to a very low temperature, are unable to move apart from one another.
They lack the motivation to do so. At this temperature, they start to group together, enter the same energy levels, and become similar to one another, acting as a single atom as a whole.
They practically form and behave as a single quantum mechanical entity at the temperature at which this Bose-Einstein condensate is cooled.
Therefore, when a gas is cooled down to an extremely low temperature, the Bose-Einstein condensate develops.

Hence, the correct answer is option C.