Read the following text and and answer the following questions on the basis of the same :
In the school project Sheetal was asked to construct a triangle and name it as ABC. Two angles A and B were given to equal to `tan^(-1)""(1)/(2)` and `tan^(-1)""(1)/(3)` respectively.

`cos(A+B+C)=`

Options

A. `1`
B. `0`
C. `-1`
D. `(1)/(2)`

Answer

C