If ABC is an equilateral triangle and D is a point of BC such that AD ⊥ BC, then

Answer: Option C

According to question,

In equilateral triangle 'AD' bisects the BC in two equal parts.
Let side of equilateral triangle is 2 cm
$$\begin{array}{rl}& \therefore \frac{AB}{BD}=\frac{2}{1}\\ & AB:BD=2:1\end{array}$$