B

a) \(\dfrac{3}{5}\) và \(\dfrac{5}{6}\) là phân số tối giản

\(\dfrac{25}{30}=\dfrac{25:5}{30:5}=\dfrac{5}{6};\dfrac{9}{15}=\dfrac{9:3}{15:3}=\dfrac{3}{5}\)

\(\dfrac{10}{12}=\dfrac{10:2}{12:2}=\dfrac{5}{6};\dfrac{6}{10}=\dfrac{6:2}{10:2}=\dfrac{3}{5}\)

b) \(\dfrac{3}{5}=\dfrac{9}{15}=\dfrac{6}{10}\) và \(\dfrac{5}{6}=\dfrac{25}{30}=\dfrac{10}{12}\)

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