A charged ball $B$ hangs from a silk thread $S$ which makes an angle $\theta$ with a large charged conducting sheet $P$, as shown in the figure. The surface charge density $\sigma$ of the sheet is proportional to:

1. A
   $\cos \theta$
2. B
   $\cot \theta$
3. C
   $\sin \theta$
4. D
   $\tan \theta$