Considering advances in science, what might be a more reliable way to classify organisms

Here's one way to follow the scientific method. place the missing steps in the correct position in the process.

What chemical speeds up the process of decomposition in dead organisms are exposed to it? nitrogen oxygen hydrogen chlorine

Which of the following can occur to two segments of a population if they are geographically isolated 1.) they can only share some types of genes 2.)both groups most likely become extinct 3.)they find a way to come back together 4.)eventually they become separate species