The major difference between angiosperms and gymnosperms comes from the

Reproductive structures and seeds.

Explanation:

In angiosperms, the reproductive structures are flowers and seeds are contained in a dispersal structure (ovary) that then becomes a fruit. On the other hand, gymnosperms have naked seeds which are not contained in a fruit. Also, angiosperms develop flowers while gymnosperms don't.

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.