Answer:
2. the line separating Australian animal species from non-Australian species
Explanation:
The Wallace line is an animal boundary line drawn by Alfred Wallace that separates Australian fauna species from non-Australian fauna species. It's a transitional zone between Austrialia and the Asia continent. The animals found in south East Asia is so much different from those found in Australia, hence the line drawn. The line is just one of the many biogeographical borders in the world separating geographical regions with not so similar group of plants and animals. 
 
        
                    
             
        
        
        
Answer:
La presión del agua es una de las razones.
Explanation:
Una gran razón de esto es la presión presente en el agua. El agua es más pesada que el aire, por lo que a presiones más profundas se vuelve más difícil para ciertos animales funcionar. Para dar cuenta de esto, muchos organismos y plantas dentro del agua se desarrollan para no tener esqueletos, ciertos órganos y otras partes del cuerpo que limitan su existencia en el agua. Las medusas son un buen ejemplo de esto.
 
        
             
        
        
        
Answer:
D) the steady, clocklike decay of certain radioactive isotopes over time.
Explanation:
Geologists use radiometric dating to estimate how long ago rocks formed, and to infer the ages of fossils contained within those rocks. 
For example, when rocks are formed, such as igneous rocks (formed when molten rocks cools), certain radioactive atoms are trapped inside the rocks during this formation process. Then these radioactive atoms decay over time.
The age of the rock can be estimated by comparing the occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.
From the options;
A) this is about the formation of the radioactive molecules and not about radiometric dating
B) this is radiocarbon dating (cabon dating/carbon-14 dating)
C) the <em>assumption </em>is wrong since the radioactive isotopes decays not accumulate.
D) the corect option as I explained earlier.