"United States" is a country name that requires the definite article "the" because it refers to a specific group of states forming a nation.
Correct usage: "the United States."
"Unjustified dream" begins with a vowel sound (the "u" in "unjustified" is pronounced as "uh"). Before vowel sounds, the correct article is "an".
Correct usage: "an unjustified dream."
The correct answer is (C) the, an.