VOA慢速英语:伊朗否认击落乌克兰飞机

on board - n. in or on a plane, train, boat...

indicate - v. to show (something): to show that (something) exists or is true

source - n. someone or something that provides information

aviation - n. the business or practice of flying

certainty - n. a fact about which there is no doubt

classified - adj. kept secret from all but a few people in government

merciful - adj. Kind and forgiving; not cruel or harsh; having or showing mercy

prefer - v. to like better or best

sanctions - n. economic or military measures designed to force a nation to do something or stop doing something

participate - v. to take part

preliminary - adj. coming before the main part of something