One of this _______ duties is to keep a record of all ___________ wages.

1. agency's employee's
2. angency's employees'
3. agencies' employees
4. agency's employees

agency's employees'

To determine the correct option, let's break down the sentence and analyze the possessive form of "agency's employees'."

The word "agency's" indicates that we are referring to something belonging to or related to the agency. Since the word "employees" is not possessive in itself, we need to add an apostrophe and an "s" to make it possessive.

Now, let's look at the usage of the apostrophe to indicate possession:

- When a singular noun (like "agency") ends with an "s," we add an apostrophe and another "s" after it.
- When a plural noun (like "employees") ends with an "s," we only add an apostrophe after it.

Applying these rules, we can form the possessive form "agency's employees'."

Therefore, the correct option is 2. agency's employees'.