Germany resumed unrestricted submarine warfare.
Your answer is false he did not :)
The one that did not contributed to the end of Pax Romana would be : D. Frequent revolts by units of the roman army led to the murder of many roman emperors.
The 3 that contributed to the end of pax romana was :
- Plaque that killed a massive number of people
- division of empire
- Barbarian Invasions
Hope this helps