Answer:
Option A, pathogen A
Explanation:
ID50 is a way to measure the virulent efficiency of a pathogen. ID50 for a pathogen depicts the number of pathogens required to infect or cause the associated disease with in 50 percent of any population sample. 
This means that 50 pathogens A can infect 50 percent  of any sample population.
While 1000 pathogen B and 1000000 pathogen C are required to infect 50 percent  of any sample population.
hence, Most virulent pathogen is Pathogen A
 
        
             
        
        
        
The magnetic vehicles will move closer to each other because the magnetic force will pull the vehicles together.
        
             
        
        
        
Answer:
The small population of zooplankton have an unequal effect on the marine community.
Explanation:
According to this question, there are three trophic levels of organism in a lake as follows: non-native fish, zooplankton, and algae. However, due to the declination in the number of zooplanktons in the lake as they were fed on by the non-native fish, the algal population increased to form a BLOOM. 
This bloom of algal species can be attributed to the lack of zooplanktons, which represented the only herbivorous (plant eaters) organism in that community. Hence, their relatively small population have an unequal effect on the marine community. This means that the small population of zooplanktons caused an imbalance in the community and this is why ZOOPLANKTON is the keystone species in this scenario.
 
        
             
        
        
        
Answer:Osmosis occurs until the concentration gradient of water goes to zero or until the hydrostatic pressure of the water balances the osmotic pressure
Explanation: