In triangle ABC a straight line parallel to BC intersects AB and AC at D and E respectively. If AB = 2AD, then DE : BC is

Answer: Option C

According to question,

Given :
AB = 2AD
$$\frac{AB}{AD}=\frac{2}{1}$$
By applying B. P. T
$$\begin{array}{rl}& \frac{AD}{AB}=\frac{DE}{BC}=\frac{AE}{AC}\\ & \frac{DE}{BC}=\frac{1}{2}\\ & \therefore DE:BC=1:2\end{array}$$