A force $\overrightarrow{\mathrm{F}}=\mathrm{\alpha }\hat{\mathrm{i}}+3\hat{\mathrm{j}}+6\hat{\mathrm{k}}$ is acting at a point $\overrightarrow{\mathrm{r}}=2\hat{\mathrm{i}}-6\hat{\mathrm{j}}-12\hat{\mathrm{k}}$ The value of $\mathrm{\alpha }$ for which angular momentum about origin is conserved is :

• A

  1

• B

  -1

• C

  2

• D

  zero