1. If you were reporting on having attended an exhibition last summer, what sentence would you choose as your most natural style of usage? (eg, like saying ‘I went to the ball game…’ or whatever comes naturally)
i tend to think of an exhibition as specific to one collection, eg the Tutankhamen exhibition that passed through Los Angeles when i was a wee one. On that premise, i'd say "I saw an exhibition last summer"
2. If someone had kept you waiting for a meeting outside a shop, say, what sort of construction would you use if reproving them about their final arrival (please incorporate a variant of those last two words)
As a matter of common courtesy, I would be loath to reprove anyone who had kept me waiting (if they had any manners, they'd have apologized upon their eventual arrival, thus obviating my need to point it out; and if they had not the proper breeding as to proffer an apology, i would not presume to take it upon myself to embark on that endeavor).
That being said, i have never found myself in the situation where i would be called upon to reprove someone for being late, since [regrettably] it is *always* me who arrives late. Hypothetically, i suppose i would simply say "I'm sorry your late arrival will force me to keep this meeting brief, as i have other commitments this afternoon".
~b