翻译：“和平与发展是当今世界的主题”

应该是：Peace and development is the theme of the modern world. 因为peace and development是作为一个整体讲的，谓语动词应用单数，否则就应该说“Peace and development arethe themes of the modern world.” 即在theme后面加s了 ，翻译时应保持主谓一致。

Peace and development are the theme of today's world

Peace and development are two major subjects in the current world.