Let −6π<θ<−12π. Suppose α1 and β1 are the roots of the equation x2−2xsecθ+1=0, and α2 and β2 are the roots of the equation x2+2xtanθ−1=0. If α1>β1 and α2>β2, then α1+β2 equals to
a. 2(\sec \theta - \tan \theta)
b. 2 \sec \theta
c. -2 \tan \theta
d. 0