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

The haemoglobin content per 100 ml of blood of a normal healthy human adult is

If due to some injury the chordae tendinae of the tricuspid valve of the human heart is partially non-functional, what will be the immediate effect?

Which two of the following changes (i $$-$$ iv) usually tend to occur in the plain dwellers when they move to high altitudes (3, 500 m or more)?
(i)  Increase in red blood cell size
(ii)  Increase in red blood cell production
(iii)  Increased breathing rate
(iv)  Increase in thrombocyte count
Changes occurring are