1. Talks are under way to toughen trade restrictions. 加强贸易限制的会谈正在进行中。
2. They jab tree trunks to toughen their hands and practice squatting with other students sitting on their shoulders to build the leg strength. 他们猛击树干来锻炼双手，练习蹲坐，让其他同学坐在他们的肩膀上锻炼腿部力量。
3. Nevertheless, researchers have discovered that a process long known to discolor and toughen foods may also contribute to age related impairment of both cells and tissues. 然而，研究人员发现，一个长期以来众所周知的使食物变色和变硬的过程也可能与年龄相关的细胞和组织损伤有关。
4. This experience will toughen her. 这次经历会让他变坚韧。
5. It is not too late for him to toughen up. 现在采取强硬的措施尚未为时过晚。
