回答内容如下:
1.Two atoms of hydrogen combine with one atom of oxygen to form a molecule of water.两个氢原子和一个氧原子结合组成一个水分子。
2.Atoms of iron in the nail combine with atoms of oxygen from the air to form molecules of iron oxide, or rust.钉子里的铁原子与空气中的氧原子结合后形成氧化铁分子，也就是锈。
3.You should try to combine exercise with a healthy diet.你应该把锻炼和健康饮食结合起来。
combine意思是“联合，合并”。We should combine studying with our friendships.我们应当把学习与我们的友谊联系起来
