The correct answers are:
A) Accepting religious toleration
Modern Nation-States are based in a common set of symbols and cultural features that generate an identity bond among their population known as Nation. In order to successfully extend this identity among the people, the nation must prevail over other identities related to non-national aspects, like religion. For that reason, religious toleration was encouraged by governments throughout history, in order to keep the people united under the same national link and avoid internal conflicts.
C) Standardizing weights and measures
In ancient times there were different ways to measure and weight even within the same state, which caused miscommunication problems among the citizens. In the modernity, the policy of standardizing weights and measures was a way to generate a common language for measures and strengthen the unity of the nation.
D) Unifying the legal code
In many former multinational empires there used to coexist different legal systems for each religious or ethnic communities. After the rise of national identity during modern times, establishing one unique legal code for all national citizens, beyond their particular religious or ethnic link, was an effective way to strengthen the national identity.