Fill up the blanks in the following paragraph by selecting the correct option.
The vascular system of the frog is a well-developed __ $\left(\mathrm{A}\right)$ __ type. The blood vascular system involves the heart, blood vessels, and blood. The heart has 3 chambers, two atria, and one ventricle, and is covered by a membrane called __ $\left(\mathrm{B}\right)$ __. A triangular structure called __ $\left(\mathrm{C}\right)$ __ joins the right atrium.

	$\mathit{A}$	$\mathit{B}$	$\mathit{C}$
(i)	open	conus arteriosus	neurilemma
(ii)	closed	sinus venosus	pericardium
(iii)	open	neurilemma	conus arteriosus
(iv)	closed	pericardium	sinus venosus