Urea reacts with water to form a compound which will decompose to form another compound. When passed through Cu²⁺(aq), a deep blue-colored solution C is formed. What is the formula of C from the following:
a) Cu(NO₃​)₂​
b) CuSO₄​
c) Cu(NH₃​)₄²⁺​
d) Cu(OH)₂​