A brief reading of the sentences suggests that the paragraph is about great inventions, focusing on the importance of scientific method and how it forms the foundation for other great inventions. 32 forms an introductory pair that claims that the modern scientific method must be the greatest of all inventions and then talks about its mode of inquiry. 1 then presents an invention that could solve many problems in the future. 4 then claims that the invention would have been impossible if the scientific method did not precede it. Hence, the coherent arrangement is 3214.