Which country includes part of the asian mainland and part of a large island?

Malaysia. It occupies part of the Malay Peninsula and part of the island of Borneo.

I'm pretty sure it's c. extremely gradual but not 100% sure though.

Magma forms by partial melting of upper mantle and crust. partial melt means that only a fraction of the available material forms a melt, and that the remainder stays solid. the partial melt rises because of its lower density and ascends through he crust. this is so conclusive mean the answer would be magma igneous rocks or balistic magma.