Fill in the blanks.
(a) In mammals, the ………… is divided into four parts.
(b) The heart ………… continuously.
(c) The vessels carrying blood from the heart to the different parts of the body are called ………… .
(d) The vessels carrying blood from the parts of the body to the heart are called ………… .
(a) In mammals, the heart is divided into four parts.
(b) The heart throbs continuously.
(c) The vessels carrying blood from the heart to the different parts of the body are called arteries.
(d) The vessels carrying blood from the parts of the body to the heart are called veins.