宰相必须从地方官员中选拔，猛将必须从士兵中产生

The concept of NP-completeness has provided a powerful tool for understanding the complexity of computational problems.

All the other children at my school are stupid. Except I’m not meant to call them stupid, even though this is what they are.

老虎起跳之前,必须先趴下蓄力然后才跳起来。

青年是国家未来的主人。全党全民必须关心、教育和培养他们。