On what date did the first Mexican truck roll across the border, bound for Dallas?

Answer: B — October 21, 2011

The correct date for the first Mexican truck rolling across the border, bound for Dallas, is significant in the context of trade and transportation policy between the United States and Mexico. October 21, 2011, marks an important milestone as it was the first time trucks from Mexico were allowed to deliver goods directly to U.S. destinations under the terms of a pilot program following years of restrictions. This event represented a shift in cross-border trade relations, aimed at enhancing efficiency and reducing costs associated with hauling goods between the two countries. This moment was particularly noteworthy as it came after considerable negotiation and regulatory adjustments. The pilot program was a response to complaints from the U.S. about the lack of access for Mexican trucks while Mexico retaliated with tariffs on certain U.S. goods. Thus, the date is significant in understanding the evolution of transportation policies and trade relations in North America. The other dates listed do not align with this key event, making the October 21, 2011, date the correct answer in the context of the question.