Question

choose three main layers of the earth. mantle crust shell nucleus mainstream core

Explanation:

The Earth has three main layers. The crust is the outermost layer. The mantle is the middle layer. The core is the innermost layer. 'Shell' is not a main layer term in geology for Earth's structure. 'Nucleus' is a term for cells or atoms, not Earth's layers. 'Mainstream' is an unrelated term.

Answer:

mantle, crust, core