During the process of a subduction, the older oceanic crust is pulled by gravity down beneath the and back into the .

Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced down into the mantle. Regions where this process occurs are known as subduction zones. Rates of subduction are typically in centimetres per year, with the average rate of convergence being approximately two to eight centimetres per year along most plate boundaries.[1]

Plates include both oceanic crust and continental crust. Stable subduction zones involve the oceanic lithosphere of one plate sliding beneath the continental or oceanic lithosphere of another plate due to the higher density of the oceanic lithosphere. That is, the subducted lithosphere is always oceanic while the over-riding lithosphere may or may not be oceanic. Subduction zones are sites that have a high rate of volcanism, earthquakes, and mountain building.

During the process of a subduction, the older oceanic crust is pulled by gravity down beneath the Trench and back into the Mantle.

i honestly speaking this is too long

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."