Answer:
The prepositional phrase in the middle of the sentence is in the middle of the exercise . This phrase modifies the verb crashed.
Step-by-step explanation:
The prepostional phrase refers to the time when the crashing of the program happened. The preposition from the phrase links the verb with the time expression middle of the exercise. If we put this question: When did the software program crash? The answer will be: In the middle of the exercise.