When ${\text{BCl}}_{\text{3}}$is strongly heated with ammonia the product formed is

• A

  ${\text{B}}_{\text{2}}{\text{H}}_{\text{6}}$

• B

  ${\text{B}}_{\text{3}}{\text{N}}_{\text{3}}{\text{H}}_{\text{6}}$

• C

  $BN$

• D

  ${\text{H}}_{\text{3}}\text{N}\to {\text{BCl}}_{\text{3}}$