電車を降りたときに帽子を忘れた。

train; electric train

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 descend (e.g. a mountain); to go down; to come down; to alight (e.g. from bus); to get off; to disembark; to dismount; to step down; to retire; to give up; to quit; to be granted; to be issued; to be given; to form (of frost, dew, mist, etc.); to be passed (from the body; e.g. of a roundworm)

by the way; incidentally; sometimes; occasionally

hat; cap

to forget; to leave carelessly; to be forgetful of; to forget about; to forget (an article)