Formal:
* The exigency of the situation demanded immediate action.
* The government invoked emergency powers due to the exigency of the crisis.
* The exigency of the mission required them to travel in secret.
* The exigency of the moment forced her to make a difficult decision.
Informal:
* The exigency of the situation meant we had to improvise a solution.
* We had to cancel the party due to the exigency of the weather.
* I had to make a quick decision due to the exigency of the moment.
Literary:
* The author's use of vivid imagery heightened the exigency of the scene.
* The play explores the exigency of human relationships in the face of adversity.
Note: "Exigency" is a formal word often used in contexts where there is a pressing need for action or a situation requiring immediate attention.