Answer:
D. to vote at all levels
Explanation:
The most important voluntary action citizens can take in a democratic society at the local, state and national levels is to vote at all levels. This means choosing eligible representatives that would represent their interest whether in the congress, house or parliament.
Voting at all levels matters. People engage with their governments through voting. They elect city council members, legislators,mayors, members of congress, governors etc are all chosen by popular vote except the president who is chosen by electoral college, which is largely determined by votes of individuals in their home state.
Vulnerable road users such as pedestrians who are engaged in work along the roadway are protected by warning signs and flashing lights. Because without those objects they might be in great danger. Through the use of those tools, drivers are aware of what's going on the roads, and that way they tend to be more careful in order to avoid any damage to the pedestrian workers.
And although it's important for workers to focus on what they are doing and pay attention to their job assignments, they can't forget about the traffic and need to be ready for any eventuality that may happen.
I think it is the German policy of unrestricted submarine warfare. All the other ones are major factors.
The Germans could now send all of their experienced troops to the Western Front. This prolonged the conflict.
B. Competition between Spanish heirs to the throne.