戸に必ず鍵をかけなさい。

door (esp. Japanese-style); entrance (to a home); narrows

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

always; without exception; necessarily; certainly; without fail; positively; invariably

key; lock

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 hang (e.g. picture); to hoist (e.g. sail); to raise (e.g. flag); to sit; to take (time, money); to expend (money, time, etc.); to make (a call); to multiply; to secure (e.g. lock); to put on (glasses, etc.); to cover; to burden someone; to apply (insurance); to turn on (an engine, etc.); to set (a dial, an alarm clock, etc.); to put an effect (spell, anaesthetic, etc.) on; to hold an emotion for (pity, hope, etc.); to bind; to pour (or sprinkle, spray, etc.) onto; to argue (in court); to deliberate (in a meeting); to present (e.g. idea to a conference, etc.); to increase further; to catch (in a trap, etc.); to set atop; to erect (a makeshift building); to hold (a play, festival, etc.); to wager; to bet; to risk; to stake; to gamble; to be partway doing ...; to begin (but not complete) ...; to be about to ...; indicates (verb) is being directed to (someone)

to do