Which organ in an adult human causes the least damage if removed?

Assertion $A$: Anemia is sometimes observed in humans.
Reason $R$: There is a deficiency of iron and copper in the human body.
Which option is correct for Assertion $A$ and Reason $R$?

Analogy type questions:
$(1)$ Fish : Single circulation :: Amphibians : ...........
$(2)$ Between right atrium and right ventricle : Tricuspid valve :: Between left atrium and left ventricle : .............

If cardiac output is $4200 \text{ ml/min}$,then $x$ beats/min is the heart rate and $y$ is the term for pulse rate.

$A$: 'Dub' is a long and sharp sound.
$R$: It is caused by the closing of atrioventricular valves.

Compare the statements $A$ and $B$.
$Statement A$: Blood sugar level falls rapidly after hepatectomy.
$Statement B$: The glycogen of the liver is the principle source of blood sugar.
Select the correct description: