If \( a \) and \( b \) are non- parallel unit vectors such that \( |\vec{a}+\vec{b}|=\sqrt{3} \), then \( (2 \vec{a}-5 \vec{b}) \cdot(3 \vec{a}+\vec{b}) \) equals- (A) \( 11 / 2 \) (C) \( -11 / 2 \) (B) 0 (D) \( 13 / 2 \)