Final answer:
Mexico is the 2nd largest buyer of LTL in the US.
Step-by-step explanation:
The 2nd largest buyer of LTL in the US is (b) Mexico.
This can be determined from the information provided in the question. It is mentioned that Mexico imports services from Japan and exports goods to Canada. Additionally, U.S. investors receive a return from past financial investments in Mexico. These facts indicate that Mexico has a significant trade relationship with the United States, making it a major buyer of Less Than Truckload (LTL) services.