Which organ remains functional for a few hours even after clinical death?

Which of the following is correct regarding blood coagulation?
$I$. Vitamin-$K$ is necessary for the formation of prothrombin.
$II$. Conversion of fibrinogen to fibrin is done by thrombin.
$III$. Conversion of prothrombin to thrombin is done by the enzyme complex prothrombinase.
The option with the correct combination is:

Which of the following statements is correct?

Plethysmograph is used to measure

What is the need for a circulatory system?

$A$: Elevated levels of $Na^+$ decrease the heart rate and contractility.
$R$: Elevated $Na^+$ levels increase the excitability of the $SA$ node.