The equation of the lines passing through the origin and having slopes $3$ and $-\frac{1}{3}$ is

Spraying of $D.D.T.$ on crops produces pollution of

If you suspect a major deficiency of antibodies in a person,to which of the following would you look for confirmatory evidence?

Name the chronic respiratory disorder caused mainly by cigarette smoking.

Consider the following statements $A$ and $B$. Identify the correct choice in the given answers.
$A$. The refractive index of the extra-ordinary ray depends on the angle of incidence in double refraction.
$B$. The vibrations of light waves acquire one-sidedness for both ordinary and extraordinary rays in double refraction.

In which of the following reactions is an aromatic aldehyde treated with an acid anhydride in the presence of the corresponding salt of the acid to give an unsaturated aromatic acid?