Apex - read the following excerpt from "ambush" by tim o'brien

i had already pulled the pin on a grenade. i had come up to a crouch. it was entirely automatic. i did not hate the young man; i did not see him as the enemy; i did not ponder issues of morality or politics or military duty. i crouched and kept my head low. i tried to swallow whatever was rising from my stomach, which tasted like lemonade, something fruity and sour.

which word from the excerpt best to establish the tone?

a. sour
b. grenade
c. duty
d. crouch