You just completed a campaign at your factory to organize a union. After speaking with all of the factory line workers, you were able to secure authorization cards from $25\%$ of them. What is the next step?

a$.$ Begin contract negotations with management

b$.$ Continue organizing your campaign to increase the percentage of signed authorization cards.

c$.$ Request certification from the NLRB$.$

d$.$ Proceed to an election on unionization.