これはその箱をあける鍵です。

this (indicating an item near the speaker, the action of the speaker, or the current topic); this person (usu. indicating someone in one's in-group); now; here; I (me); certainly

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

that (something or someone distant from the speaker, close to the listener; actions of the listener, or ideas expressed or understood by the listener); the; um...; er...; uh...

box; case; chest; package; pack; car (of a train, etc.); shamisen case; shamisen; public building; community building; man who carries a geisha's shamisen; receptacle for human waste; feces (faeces); counter for boxes (or boxed objects)

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to open (a door, etc.); to unwrap (e.g. parcel, package); to unlock; to open (for business, etc.); to empty; to remove; to make space; to make room; to move out; to clear out; to be away from (e.g. one's house); to leave (temporarily); to dawn; to grow light; to end (of a period, season); to begin (of the New Year); to leave (one's schedule) open; to make time (for); to make (a hole); to open up (a hole)

key; lock

be; is