The correct answer to this open question is the following.
You forgot to include the options for the question, the author's name, and the book or excerpt. However, doing some research, we can help you we this general comment.
Entering Monterrey was risky, and this can be read in the section describing the advance of Taylor's division because General Zachary Taylor had to confront and stop the Mexican Army that was led by General Pedro de Ampudia.
We are talking about the Battle of Monterrey, a bloody battle fought during the Mexican-American War. The Battle started on September 21, 1846, and ended three days later with a victory for General Taylor's troops.