Heart is the organ that pump blood throughout the body. It has various parts that have different works to do. The part of the heart that takes blood from the veins and pumps it into a ventricle is the atria, i.e. option a.
Human heart is one of the differentiating character. It is actually four chambered.
The chambers are:
These chambers are separated by valves that maintain blood flow.
Thus, the correct option is a.
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