Which one of the following reactions is fcc/bcc crystals with lattice parameter 'a' is energetically favourable?

A. $$\frac{a}{2}\left[ {\overline 1 10} \right] + \frac{a}{2}\left[ {0\overline 1 \overline 1 } \right]$$

B. $$\frac{a}{2}\left[ {111} \right] + \frac{a}{2}\left[ {11\overline 1 } \right]$$

C. $$\frac{a}{2}\left[ {115} \right] + \frac{a}{2}\left[ {11\overline 1 } \right]$$

D. $$\frac{a}{2}\left[ {111} \right] + \frac{a}{2}\left[ {111} \right]$$

Answer: Option A