Scientists have to work hard to keep _____ with modern discoveries and developments.

—Do I need to give a tip if I eat at a fast food restaurant in the United States?—Yes , it’s a common       to tip waiters in a restaurant.

Lin Dan won the first prize in the Beijing Olympics, which helped him gain the ____ of the world.

________________of the students who took part in the military training（军训） is 450．

As second-hand smoking is more harmful and dangerous, people want a total _____against smoking in public．