Final answer:
The Texans who remained at the Alamo understood that they would die if they stayed. The correct answer is option a.
Step-by-step explanation:
The best conclusion supported by the selection is that the Texans who remained at the Alamo understood that they would die if they stayed. Despite being heavily outnumbered and ignoring orders from General Sam Houston, the defenders chose to stay and fight. The fact that all of the defenders were killed, including well-known figures like Davy Crockett and William Travis, indicates their understanding of the dire situation and their willingness to sacrifice their lives for the cause of independence.