窓をあけてもいいですか。

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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 raise; to elevate; to do up (one's hair); to fly (a kite, etc.); to launch (fireworks, etc.); to surface (a submarine, etc.); to land (a boat); to deep-fry; to show someone (into a room); to summon (for geishas, etc.); to send someone (away); to enrol (one's child in school); to enroll; to increase (price, quality, status, etc.); to develop (talent, skill); to improve; to make (a loud sound); to raise (one's voice); to earn (something desirable); to praise; to give (an example, etc.); to cite; to summon up (all of one's energy, etc.); to arrest; to nominate; to give; to offer up (incense, a prayer, etc.) to the gods (or Buddha, etc.); to bear (a child); to conduct (a ceremony, esp. a wedding); (of the tide) to come in; to vomit; to do for (the sake of someone else); to complete ...; to humbly do ...

too; also; in addition; as well; (not) either (in a negative sentence); both A and B; A as well as B; neither A nor B (in a negative sentence); even; as much as; as many as; as far as; as long as; no less than; no fewer than; even if; even though; although; in spite of; further; more; again; another; the other

good; excellent; fine; nice; pleasant; agreeable; sufficient (can be used to turn down an offer); ready; prepared; profitable (e.g. deal, business offer, etc.); beneficial; OK

be; is

indicates a question (sometimes rhetorical); or; whether or not; some- (e.g. something, someone); indicates doubt, uncertainty, etc.; emphatic prefix; suffix forming adjectives or adverbs; in that way