A long solenoid of radius \(R\) has \(n\) turns per unit length and carries a constant direct current \(I\). A flat sheet is placed inside the solenoid such that its perimeter touches the inner walls of the solenoid, completely spanning the interior cross-section. The sheet is tilted so that its surface normal vector makes an angle \(\theta\) with the central longitudinal axis of the solenoid, where \(0 \le \theta < \frac{\pi}{2}\). The surface area of the tilted sheet is \(A = \dfrac{\pi R^2}{\cos\theta}\). Which of the following expressions represents the magnetic flux \(\Phi_B\) through the tilted sheet?