C
1) Examining those pairs of ratios, and simplifying them we have:
[tex]\begin{gathered} a)\text{ }\frac{9}{12}=\frac{3}{4}\ne\frac{5}{8} \\ b)\text{ }\frac{25}{30}=\frac{5}{6}\ne\frac{16}{21} \\ c)\text{ }\frac{6}{27}=\frac{2}{9} \\ d)\text{ }\frac{7}{12}\ne\frac{10}{15}=\frac{2}{3} \end{gathered}[/tex]2) After simplifying we can see that 6/27 is equivalent to 2/9 after simplifying both by 3.
3) Hence, the answer is c)