$\alpha, \beta$ are the roots of the equation $\sin ^2 x+b \sin x+c=0$. If $\alpha+\beta=\frac{\pi}{2}$ then $b^2-1=$

• A

  $c$
• Correct answer
  B

  $2c$
• C

  $c^2$
• D

  $4 c^2$

Hence, the correct answer is option: 'B'.