他的手机在玩游戏时开始卡顿。
His phone started to ___lag when playing games.
他的电脑太旧了，运行程序时总是反应迟钝。
His old computer always ___lagged when running programs.
他在数学课上总是跟不上进度。
He is always ___lagging behind in math class.
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