Answer:
Rosalind's x-ray showed that the ladders of nucleotides were inside a double helix. 
Watson and Crick built models with the ladders on the outside. 
 
        
                    
             
        
        
        
This is called Homeostasis
        
             
        
        
        
Fossils can show structural similarities and differences in organisms over time revealing the vast diversity of life forms that have and continue to exist on Earth.
Comparisons between living organisms and fossils also allow scientists to make inferences about the lines of descent.
 
        
             
        
        
        
Answer:
A model in which oak has a positive transition rate to the invasive and the invasive has a positive transition to oak.
Explanation:
An invasive species is the one which is non-native to the given ecosystem. Its growth hampers balanced ecological parameters and disturbs food web as well as normal flora.The overall effect of invasive species is decreasing biodiversity in selected ecosystem. As the ecologist needs to understand effect of this invasive species, firstly it is important to understand the transition of oak tress to invasive form. The transition rate is one of the deciding factor to introduce diversity in ecosystem. Also if the invasive form has the ability to revert back to original oak tress it would restore the original ecosystem. Thus a model in which oak has a positive transition rate to invasive and the invasive has a position transition to oak can be selected for the analysis. In other models, the final trnasition to grass would introduce lot of biodiversity in selected ecosystem which would be of little importance to understand transition rate.