Answer:
The correct option is H) these acids change the environment.
Explanation:
Soil can be described as the part of the environment where plants grow. In primary succession, life stars arising in an area which has no soil and only rocks, This is possible because lichens are the organisms which can grow on the rocks. Lichens secrete certain acids which break down these rocks and hence soil begins to form when these rocks break. This makes it possible for other plant species to grow on these lands. 
 
        
             
        
        
        
Answer: C
Explanation: All organisms someway somehow must compete for essential resources.
 
        
             
        
        
        
Answer:
16 pg at the end of S
16 pg at the end of G2
Explanation:
A cell has 8 pg of DNA per nucleus in G1.
During S phase the DNA replicates, so every nucleus will contain double the normal amount of DNA that was present in G1. Therefore, at the end of S each nucleus would have 16 pg of DNA.
During G2 the cell continues growing and preparing for mitosis, but DNA content does not change: there are still 16 pg per nucleus.