What does the SI Metric System primarily rely on?

The SI Metric System, also known as the International System of Units, primarily relies on seven internationally recognized base units. These base units define standard measurements for fundamental quantities in science and engineering. The seven base units are meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity).

Each of these units is well-defined and serves as the foundation for derived units, which can encompass a wide range of measurements used in various fields. The usage of a set number of base units facilitates uniformity and consistency across scientific disciplines, making communication of measurements clear and precise globally.

In contrast, the other options imply a different structure that does not accurately reflect the established framework of the SI system. For instance, two standard units might refer to a simple system but does not correspond to the comprehensive structure of SI. Similarly, ten unique measurements or fifteen variable units would not align with the officially recognized approach, which is focused on the seven foundational units that have been internationally standardized.