I apologize for the confusion. You're right, there are three simple sentences among the four options. The other two simple sentences are:
1. Given the time of day, we were lucky to find a taxi.
This sentence has one independent clause: "we were lucky to find a taxi." The phrases "given the time of day" and "to find a taxi" are modifiers within the sentence.
3. Eventually she will.
This sentence also has one independent clause: "she will." The word "eventually" is an adverb modifying the verb "will."
So, in total, there are three simple sentences: 1, 3, and 4.