What rule applies most closely to this word exhaust-?

The rule that applies most closely to the word "exhaust-" is the rule of adding "-ed" to verbs to form the past tense.

Here's why:

* "Exhaust" is a verb. It means to use up completely or tire out.

* Adding "-ed" to the verb "exhaust" creates the past tense: "exhausted"

Example:

* Present tense: I exhaust myself with work.

* Past tense: I exhausted myself with work yesterday.

While there are other rules for forming past tenses, this one applies directly to the word "exhaust-" as it creates a regular past tense form.