Which type of circulatory system is shown in the given figure?

In a portal system of man:

The circulatory pattern,in which blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses,is called $.......$ and it is found in $........$

What type of circulatory system is present in a frog?

What is characteristic of birds $(Aves)$ and mammals?

Identify whether the given statements are true or false for double circulation.
$I$. It prevents the mixing of oxygenated and deoxygenated blood in the heart.
$II$. It circulates only oxygenated blood through the heart.
Choose the correct option accordingly.