Assertion A : If A, B, C, D are four points on a semi-circular are with centre at 'O' such that
\left|\right. \overset{\rightarrow}{A B} \left|\right. = \left|\right. \overset{\rightarrow}{B C} \left|\right. = \left|\right. \overset{\rightarrow}{C D} \left|\right., then
\overset{\rightarrow}{A B} + \overset{\rightarrow}{A C} + \overset{\rightarrow}{A D} = 4 \overset{\rightarrow}{A O} + \overset{\rightarrow}{O B} + \overset{\rightarrow}{O C}Reason R : Polygon law of vector addition yields
\overset{\rightarrow}{A B} + \overset{\rightarrow}{B C} + \overset{\rightarrow}{C D} + \overset{\rightarrow}{A D} = 2 \overset{\rightarrow}{A O}In the light of the above statements, choose the most appropriate answer from the options given below :