Just a reminder, don't read the question wrong (it is AB=2AD, many people regard it as AB=2CD, and some people regard ellipse as hyperbola).

Let AB=2 and AD= 1.

For hyperbola, according to the definition, c= 1 (half focal length), D is on hyperbola, BD-DA=2a, then a=(BD- 1)/2, then E1= C/A = 2/(BD-/kloc-0

For an ellipse, according to the definition, c=CD/2, A is on the ellipse, and AD+AC=2a, then A = (AC+1)/2 = (BD+1)/2, and E2 = C/A = CD/(BD+/kloc-0).

E1e 2 = 2cd/((BD-1) (BD+1)) = 2cd/(BD 2-1), CD=AB-2ADcosθ=2-2cosθ, and BD is determined by cosine theorem.

Choose B.