original: many specialize in machine construction , medical equipment , international trade , optics and electronics .
simplifications: some focus on building machines , medical equipment , international trade , optics , and electronics . many people are experts in machine assembling , medical instruments , trade between different countries , optics -lrb- the scientific study of sight and the behavior of light -rrb- and electronics . many specialize in machine building , medical equipment , international trade , optics and electronics . many specialize in machine construction zones . many specialize in machine construction , medical equipment , international trade , optics and electronics . several specialize in machine construction , medical equipment , international trade , optics and electronics . many are good in machine building , medical tools , international trade , optics and electronics . many specialize in machine construction , medical equipment , international trade , optics and electronics .