[tex]\it \dfrac{a}{b}=\dfrac{3}{7} \Rightarrow a=3k,\ \ b=7k\\ \\ \\ \dfrac{c}{d}=\dfrac{3}{7} \Rightarrow c=3m,\ \ d=7m\\ \\ \\ \dfrac{a+c}{b+d}=\dfrac{3k+3m}{7k+7m}=\dfrac{3(k+m)}{7(k+m)}=\dfrac{3}{7} \Rightarrow c)\ este\ singura\ adev\breve arat\breve a[/tex]
