bì xū
学习必须刻苦钻研。
Xuéxí bìxū kèkǔ zuānyán.
Learning must involve diligent study and research.
明天你必须来。注意（适用于以上义项）“必须”的否定是“无须”、“不须”或“不必”。
Míngtiān nǐ bìxū lái. Zhùyì (shìyòng yú yǐshàng yì xiàng) "bìxū" de fǒudìng shì "wúxū", "bùxū" huò "bùbì".
You must come tomorrow. Note (applicable to the above meanings) the negation of "must" is "no need", "not necessary" or "need not".