Which of the following is a way for a state to achieve international sovereignty?
a. declare sovereignty in a document, such as the declaration of independence
b. pass a law requiring other states to recognize its sovereignty
c. gain recognition of sovereignty from the united nations
d. merge with another state and form a new state
select the best answer from the choices provided.

Let's go through the options:
a. declare sovereignty in a document, such as the Declaration of Independence
-this is a good start, but it's not enough, a number of states have declared sovereignty but they were not recognized internationally. 

b. pass a law requiring other states to recognize its sovereignty
- a state can't pass a law about what the others should do: this is a false answer

c. gain recognition of sovereignty from the United Nations
-this is the best way of achieving sovereignty in a way that is recognized internationally - this is the best answer.

d. merge with another state and form a new state
-this is not the right answer - this state would not be sovereign then.