(a) Number 3 represents the heart as it is receiving two blood vessels : 9 (venacava) & 4 (pulmonary vein) , and also two blood vessels are emerging out from it : 1 (pulmonary artery) & 5 (aorta).

Venacava is the blood vessel which brings blood to the heart from upper & lower parts of the body.

Pulmonary vein is the blood vessel which brings in oxygenated blood from lungs to left auricle.

Pulmonary artery is the blood vessel which carries de oxygenated blood from right ventricle to lungs.

Aorta is the blood vessel which carries oxygenated blood from left ventricle to all parts of the body.

(b) The following numbers represent the following respectively

1 : Pulmonary artery (as it is carrying blood from heart to lungs)

5 : Aorta (as it is carrying blood away from heart to other body parts)

7 : Hepatic portal vein (as it is carrying blood from intestine to liver for detoxification)

8 : Renal vein (as it is carrying de oxygenated blood from kidneys to heart)

9 : Superior venacava (as it is carrying de oxygenated blood from upper parts of the body to the heart)

10 : Stomach (as blood passes from both stomach and intestine to the liver)

11 : Dorsal Aorta (blood vessel which carries oxygenated blood from left ventricle to all parts of the body)