Heart lacks sinus venosus in

What is sinus venosus?

____Node may be regarded as a remnant of sinus venosus is mammalian heart.

Three chambered heart with sinus venosus, moist skin without scale and tympanum represents ear, are characteristics feature of :

[A] : In amphibians heart is two chambered. [R]: The oxygenated blood is returned to the heart through sinus venosus.

[A] : in amphibians heart is two chambered. [R]: The oxygenated blood is returned to the heart through sinus venosus.

[A] : in amphibians heart is two chambered. [R]: The oxygenated blood is returned to the heart through sinus venosus.

[A] : in amphibians heart is two chambered. [R]: The oxygenated blood is returned to the heart through sinus venosus.

A: In frog, sinus-venosus is present. R: In mammals and birds are remnant of sinus venosus has taken part in the formation of SA node.

What is correct about sinus venosus