From which of the following can a milk-like substance be prepared?

When an unpolarized light of intensity $I_0$ is incident on a polarizing sheet,the intensity of the light which does not get transmitted is

The length of the latus rectum of the parabola $y^2+8x-2y+17=0$ is

The polar equation of the line perpendicular to the line $\sin \theta - \cos \theta = \frac{1}{r}$ and passing through the point $\left(2, \frac{\pi}{6}\right)$ is

The joint equation of two lines passing through the origin,each making an angle of $30^{\circ}$ with the $Y$-axis,is

In each of the following,determine whether the statement is true or false. If it is true,prove it. If it is false,give a counterexample.
If $x \in A$ and $A \in B,$ then $x \in B$.