Answer:
A. Most European nations wanted to avoid war at all costs.
Step-by-step explanation:
This is the main reason why Hitler was allowed to continue his aggression without resistance from other European countries at the beginning of the war. Other European powers were aware of the fact that Hitler was not going to stop easily. Therefore, they knew that if they were to intervene, the war would probably become much more complex and destructive, and most nations wanted to avoid this at all costs.