The subjunctive mood is the best.
The subjunctive is rarely used in colloquial English. Totally irrelevant information, but... it is a relic from Latin, where there are many uses for a subjunctive. There is even a special conditional using the subjunctive mood that expresses the exact circumstances you described, which is usually called future less vivid.
In horror, or any other word that means 'in fright.'
If these were the missing choices:
<span>A) Farquhar may unknowingly walk into a trap.
B) Farquhar will pursue the soldier from the North.
C) Farquhar and the soldier may engage in an altercation.
D) Farquhar and his wife will forget about the soldier
</span>
My answer is : A) <span>Farquhar may unknowingly walk into a trap.
Farquhar is a confederate supporter. That is why when he saw a confederate soldier, he reported of Union movements in the hopes that the Union soldiers will be defeated in the Civil War. Unfortunately, the Confederate soldier was in fact a Union soldier in disguise. </span>
Noun1.the subject of a talk, a piece of writing, a person's thoughts, or an exhibition; a topic."the theme of the sermon was reverence"