The final stage of drug addiction is represented by the need of drug for the body. This is known as

Addiction to alcohol causes

Identify the molecules $(A)$ and $(B)$ shown below and select the right option giving their source and use.

Molecule             $\to $         Source                  $\to $                Uses

The harmful allele of sickle cell anemia has not been eliminated from human population. Such afflicted people derive some other benefit. Discuss.

Tunnel vision is caused by