In the reaction :   ${\mathrm{BF}}_3 + 3{\mathrm{LiBH}}_4 \stackrel{ }{\to } 3\mathrm{LiF} + \mathrm{X}; \mathrm{X} \mathrm{is}$

• A

  ${\mathrm{B}}_4{\mathrm{H}}_{10}$

• B

  ${\mathrm{BH}}_3$

• C

  ${\mathrm{B}}_2{\mathrm{H}}_6$

• D

  ${\mathrm{B}}_3{\mathrm{H}}_8$