\(\text{Assertion A}\) : If \(A,~B,~C,~D\) are four points on a semi-circular arc with centre at \('O'\) such that \(|\overrightarrow {AB}|=|\overrightarrow {BC}|=|\overrightarrow {CD}|\), then \(\overrightarrow {AB}+\overrightarrow {AC}+\overrightarrow {AD}=4~\overrightarrow {AO}+\overrightarrow {OB}+\overrightarrow {OC}\)
\(\text{Reason R}\) : Polygon law of vector addition yields
\(\overrightarrow {AB}+\overrightarrow {BC}+\overrightarrow {CD}=\overrightarrow {AD}=2~\overrightarrow {AO}\)
In the light of the above statements, choose the most appropriate answer from the options given below :