"They are going up to fill them in straight away." in French

Ils montent les remplir tout de suite.

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Literal Breakdown

English	French	Learn
they (masculine)	ils	Learn
go upstairs; are going upstairs (3rd person plural)	montent	Learn
them (direct object)	les	Learn
to fill in	remplir	Learn
immediately; right away	tout de suite	Learn

The French translation for “They are going up to fill them in straight away.” is Ils montent les remplir tout de suite.. The French, Ils montent les remplir tout de suite., can be broken down into 5 parts:"they (masculine)" (ils), "go upstairs; are going upstairs (3rd person plural)" (montent), "them (direct object)" (les), "to fill in" (remplir) and "immediately; right away" (tout de suite).