Answer:
The cause for men to be lurking in darkness and what possible threat they pose to Portia and Brutus.
Step-by-step explanation:
An external conflict is when there is a dilemma in the character, posing an obstacle for the development or success of that character. It is external in the sense that it involves an external force whether it be in the form of another character or natural forces, as opposed to the character and his feelings.
In the given excerpt from "The Tragedy of Julius Caesar" by William Shakespeare, we can assume that the external conflict that Portia wants her husband to tell her is the cause for men to lurk in the darkness and what threat they pose for the couple. Besides, the other three options only present an inner conflict in Brutus, which rules them out of the equation.
Thus, the correct answer is the third option.