Answer:
Option a. 204 degree
Explanation:
see the attached figure to better understand the problem
we know that
The semi-inscribed angle is half that of the arc it comprises.
so
∠B=(1/2)[arc BC]
substitute
78°=(1/2)[arc BC]
arc BC=156°
Remember that
arc BC+arc BCD=360°
arc BCD=360°-156°=204°