If A and B together can complete a piece of work in 20 days, B and C in 10 days and C and A in 12 days, then A, B and C together can complete the same work in :
[A] $4\frac{2}{7}\ days$
[B] $\frac{7}{60}\ days$
[C] $8\frac{4}{7}\ days$
[D] $30\ days$