Which numbering system uses only two digits?

The numbering system that uses only two digits is Base 2, also known as the binary system. In this system, the only digits used are 0 and 1. Each digit represents a power of two, which is the foundational principle behind binary counting and digital electronics.

For example, in binary, the number "10" actually represents the decimal number 2 (12^1 + 02^0). This simplicity allows computers and electronic devices to use the binary system efficiently, as it corresponds to the two states of electronic switches: on (1) and off (0).

The other numbering systems mentioned use more than two digits. Base 10 uses ten digits (0 through 9), Base 16 uses sixteen digits (0 through 9 and A through F), and Base 8 uses eight digits (0 through 7). Each of these systems serves different purposes and represents numbers in their own way, but only Base 2 exclusively relies on just the two digits, making it unique among the options provided.