currency option

John, in trade option, from the table, that are few available exercise price to choose, however, how and which exercise price will chosen, i know if the exercise price which is favourable, but sometimes, when i doing the question, i am difficult to choose which exercise need to be use. i know calculate the option contract number, which call or put, but when come to the which exercise price, it is harder, because sometimes the question is home currency same or home currency different, and receipt or payment make it confuse me alot when choose the exercise price.