翻译下面四个句子,并写出划线词的意思。 1 、 Proper application of these machine elements depends upon knowledge of the force on the structure and the strength of the materials employed. 2 、 The hardness of a gear determines its ability to resist wear . 3 、Manufacturing engineers have centered their efforts on the development of standardized elements . 4 、 These parts are produced in large quantities with a high degree of perfection at reduced cost .