Which excerpt from a rumor of war best illustrates vietnam's uncomfortable climate

Here is the excerpt from A Rumor of War which best illustrates Vietnam's uncomfortable climate:
The tedium was occasionally relieved by a large-scale search-and-destroy operation, but the exhilaration of riding the lead helicopter into a landing zone was usually followed by more of the same hot walking, with the mud sucking at our boots and the sun thudding against our helmets while an invisible enemy shot at us from distant tree lines.