Write the name of the period that has the digits 913.

The answer is the thousands period.

Explanation:

Periods of numbers are sets of three digits that are separated by commas when written in standard form.

The period at the right end of a number is the hundreds period; it includes the place values ones, tens, and hundreds.

The period to the left of the hundreds period is the thousands period; it includes the place values thousands, ten-thousands and hundred-thousands.  In this number, 9 is in the hundred-thousands place, 1 is in the ten-thousands place, and 3 is in the thousands place; this puts 913 in the thousands period.