Instruction:
How many strings does a bass guitar have?

Response:
Most bass guitars have four strings.  Because the bass is designed for lower frequency than standard (usually six-string) guitars, the bass guitar strings are thicker and heavier than standard guitar strings.

Some basses are made with five or even six strings.  This allows the bassist to hit higher or lower notes than the standard bass guitar range, which can allow more creative freedom.  Four strings is still considered the standard for bass guitars, though.