You wrote:
""we can use horn, when overtaking a vehicle outside the built up area, only when there is an immediate danger"".

That is not written on the theory page.
You use a bad translator machine.

Don't make your own answers.
C is correct.
Stop putting images.

we can use horn, when overtaking a vehicle outside the built up area, only when there is an immediate danger. in the question, there is not an immediate danger and it is asked whether we can use the horn when overtaking the car. The Answer is, yes I can outside the built up area.
since there is not an immediate danger, should the answer be "NO"