冷蔵庫のドアを開いたらリンゴが落ちた。

refrigerator

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

door (Western-style)

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; to undo; to unseal; to unpack; to bloom; to unfold; to spread out; to open (for business, e.g. in the morning); to be wide (gap, etc.); to widen; to hold (meeting, etc.); to give; to open; to found (nation, dynasty, sect, etc.); to open (a new business); to set up; to establish; to start; to open (ports, borders, etc.); to open (an account); to open up (new land, path, etc.); to clear; to develop; to open (a file, etc.); to extract (root); to reduce (equation); to cut open (fish); to change (kanji into hiragana); to flare (e.g. skirt); to slacken (into a poor posture)

apple (fruit); apple tree (Malus pumila)

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to fall down; to drop; to fall (e.g. rain); to sink (e.g. sun or moon); to fall onto (e.g. light or one's gaze); to be used in a certain place (e.g. money); to be omitted; to be missing; to decrease; to sink; to fail (e.g. exam or class); to lose (contest, election, etc.); to crash; to degenerate; to degrade; to fall behind; to become indecent (of a conversation); to be ruined; to go under; to fade; to come out (e.g. a stain); to come off (e.g. makeup); to be removed (e.g. illness, possessing spirit, name on a list); to fall (into someone's hands); to become someone's possession; to fall (into a trap); to fall (for a trick); to give in; to give up; to confess; to flee; to fall; to be defeated; to surrender; to come to (in the end); to end in; to fall (in love, asleep, etc.); to swoon (judo); to consent; to understand; to crash; to freeze; to die; to move to the depths