Which of the following countries announced its exit from the Trans Pacific Partnership (TPP) in January 2017?

Introduction / Context:
This question concerns international trade agreements and recent geopolitical developments. The Trans Pacific Partnership, or TPP, was a major proposed trade agreement among several Pacific Rim nations. In January 2017, a significant event occurred when one major country withdrew from the agreement, creating wide media coverage and exam relevance.

Given Data / Assumptions:

• The agreement in question is the Trans Pacific Partnership, abbreviated as TPP.
• The time frame is January 2017.
• The options are Japan, USA, Mexico and Brunei.

Concept / Approach:
The USA, under the new administration in January 2017, decided to withdraw from the TPP, arguing that it did not sufficiently benefit American workers. This decision was announced soon after the new President took office and became a major headline in global trade news. Japan, Mexico and Brunei remained in the grouping that later moved towards alternative structures without the USA. Thus, the correct answer is the United States of America.

Step-by-Step Solution:

Verification / Alternative check:
Another verification method is to recall economic discussions from that period, where media and analysts debated the impact of United States withdrawal from the TPP on its influence in Asia Pacific trade. The withdrawal was linked to domestic political promises in the USA. No major news of Japan, Mexico or Brunei exiting at that time exists in common exam resources, which confirms that the USA is the correct response.

Why Other Options Are Wrong:
Japan: Japan stayed committed to the TPP framework and later helped promote an alternative version without the USA.

Mexico: Mexico remained a participant and did not announce an exit in January 2017.

Brunei: Brunei is a smaller member state and did not withdraw in that period.

Common Pitfalls:
Learners sometimes confuse the TPP with other agreements like NAFTA or later trade discussions involving these countries. Another pitfall is assuming that a smaller country might have left rather than the largest economy, but in reality the news significance was precisely because the largest economy in the group withdrew. Remembering that it was the USA that walked away from the TPP in early 2017 will help avoid confusion.

Final Answer:
The country that exited the Trans Pacific Partnership in January 2017 was the USA.