Read the passage.

The Humane Society of the United States [HSUS] is headquartered in Washington, DC, and was founded by a group of journalists in 1954. The organization employs 528 workers. It is the 136th-largest charity in the United States and boasts over 1,500 volunteers. The Humane Society’s mission focuses on five issues: factory farming, animal fighting, the fur trade, puppy mills, and wildlife abuse. Less than a decade ago, the HSUS began pursuing global work through an affiliate. Today there are staff members working in 17 different nations.

Which use of brackets would improve the clarity of this passage?

Less than a decade ago, the HSUS began pursuing global work [work outside of the United States] through an affiliate.
Less than a decade ago, the HSUS began pursuing global work through an affiliate [Humane Society International].
Less than a decade [eight years] ago, the HSUS began pursuing global work through an affiliate.
Less than a decade ago, the HSUS [Humane Society of the United States] began pursuing global work through an affiliate.