Plethysmograph is used to measure

What is the study of the circulatory system called?

Given below are four statements $(i-iv)$ regarding the human blood circulatory system.
$(i)$ Arteries are thick-walled and have a narrow lumen as compared to veins.
$(ii)$ Angina is acute chest pain when the blood circulation to the heart muscle is reduced.
$(iii)$ Persons with blood group $AB$ can donate blood to any person with any blood group under the $ABO$ system.
$(iv)$ Calcium ions play a very important role in blood clotting.
Which two of the above statements are correct?

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:

Consider the following four statements regarding the human circulatory system:
$(a)$ Arteries have thick walls and a narrower lumen compared to veins.
$(b)$ Angina is a sudden chest pain.
$(c)$ In the $ABO$ blood grouping system,a person with blood group $AB$ can donate blood to anyone.
$(d)$ Calcium ions play a significant role in blood clotting.
Which two of the above statements are correct?

The given figure shows the schematic plan of blood circulation in humans with labels $A$ to $D$. Identify the label and give its function/functions.