Answer:
<h2>Increase.</h2>
Step-by-step explanation:
Two-dimensional space is modelled by the coordiante system with 4 quadrants only, and the axis are x and y, the independent and the dependent variables, respectively.
On the other hand, the three-dimensional space has three coordinates, x, y and z. The extra coordinate allows to have a three-dimensional space. Also, this extra coordinate increases the number of quadrants, actually, they are called octants, becayse they are eight.
Therefore, the word missing here is "increase".
