You will be given a definition of a task first, then some input of the task.
This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Passage: With an estimated population of 1,381,069 as of July 1, 2014, San Diego is the eighth-largest city in the United States and second-largest in California. It is part of the San DiegoTijuana conurbation, the second-largest transborder agglomeration between the US and a bordering country after DetroitWindsor, with a population of 4,922,723 people. San Diego is the birthplace of California and is known for its mild year-round climate, natural deep-water harbor, extensive beaches, long association with the United States Navy and recent emergence as a healthcare and biotechnology development center. Question: Which city in Mexico does San Diego border?
Output:
Tijuana