"A sentinel at each end of the bridge stood with his rifle in the position
known as 'support,' that is to say, vertical in front of the left shoulder,
the hammer resting on the forearm thrown straight across the chest -- a
formal and unnatural position, enforcing an erect carriage of the body,
What is the meaning of the word sentinel as it is used in this sentence
from the passage?
A)
a feeling of emotion
B)
a man who stands guard
C)
a place for tools
D)
a support for a rifle

B)  a man who stands guard

Explanation:

This is an excerpt from An Occurrence at Owl Creek Bridge, a story written by Ambrose Bierce.

The meaning of the word 'sentinel' is a guard, or a lookout. 'Sentinel' is clearly not an emotion, a place or a support for a rifle, because it is easy to see from the text itself that the author is writing about a person, and not an object/emotion. The person is keeping watch, guarding someone, while his forearm and chest are mentioned in the text.

what author is in this question?

if you let me know i will let you know in the comments.