VOA慢速英语:US Denies Visas for Gambian, Afghan Robotics Teams

disappointing – adj. making someone unhappy by not being as good as expected or by not doing something that was hoped for or expected

mingle – v. to move around during a meeting, event, or party and talk informally with different people

contaminant – n. something that makes a place or a substance (such as water, air, or food) no longer suitable for use