As compared to the circulatory system of most fishes, the circulatory system of adult amphibians has the advantage of a single circuit. partially-separate circuits for gas exchange and systemic delivery of blood. complete separation between oxygenated and deoxygenated blood. a four-chambered heart. a pocket of the gut that serves as an air bladder.

Partially separate circuits for gas exchange and systemic delivery of blood.

Explanation:

Adult amphibians have separate circuits for gas exchange and systemic delivery of blood. Fishes usually breathe through gills  and very few have nostrils. The fishes can breathe underwater with the help of their gills.

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.