#### Answer

The correct answer is:
(d) As many as possible

#### Work Step by Step

To change the polarization $90^{\circ}$ with $N$ sheets, we can rotate each sheet at an angle of $\frac{90^{\circ}}{N}$ to the previous sheet.
According to Malus' law, the transmitted intensity through a polarizing sheet is given by $I = I_0~cos^2~\theta$, where $I_0$ is the intensity of the incident light.
With $N$ sheets, the final transmitted intensity is $I = I_0~(cos~\frac{\theta}{N})^{2N}$, where $I_0$ is the initial intensity. As $N$ increases, the value of this expression increases. Therefore, we should use as many sheets as possible to get maximum transmitted intensity.
The correct answer is:
(d) As many as possible