Bird migrations began with the recession of the glaciers during the ice age. You will notice a great increase in insects in the spring time and early summer.The birds moved North to take advantage of this increase in the food supply that followed the warming in the spring and early summer. Their reproductive organs temporarily developed so they could lay eggs and raise a family. Look at the early flush of Night crawlers in the moist times of the early rains. By mid summer most of the insects have matured, mated and died. Their eggs have hatched and turned to larva and moved underground until next spring. The shortening of the days causes the reproductive functions to decrease and signals the birds that the food will soon become scarce. They move back to the area that makes it the easiest to find food and avoid freezing. which of course is the warmer climates nearer the equator. Not all birds move past the Tropics at approximately 30 degrees. Some like Chickadees may move down from Mi or Mn or Canada only as far south as Indiana. Some migrations may be quite short. For example from the mountains down to the plains. They don't generally reproduce in the warmer winter climes they migrate to. In the spring time they migrate along paths of the retreating glaciers. As the climate warms away from the tropics the birds follow the emerging insects etc to the birds selected breeding grounds.with increased insects and longer days to feed the hatching's. It is necesary to understand why they move to cooler climates in the summer to under stand why they move to eh warmer ones in the fall. As the days shorten the food supply dwindles and the babies have fledged. They move to warmer climates in winter to rest and refuel for the next years migration.
        
             
        
        
        
The correct answer is indicator species.
 
        
             
        
        
        
Answer: A food chain or food web provide information on the eating patterns of organisms, how energy is transfered from one organisms to another and the flow if energy in the ecosystem.
Explanation:
Food chain is the link of network that that starts from producer to the consumer and finally ends at the predator species and decomposer species in the ecosystem. It describe the feeding relationships among organisms.
Food web contains interconnection of several food chains in the ecosystem. It shows several feeding relationships in food chains .
Both food chain and food web provide information of how organisms are interconnected, their eating patterns, how energy is transferred from one organisms to another and flow of energy in the ecosystem.
 
        
             
        
        
        
Supplements the digestive process to break down food 
Produces vitamins,short chain fatty acids and proteins utilized by the body 
Strengths immune function
Creates beneficial nutrients that prevent weight gain
        
             
        
        
        
Hi there!
We can go through the overall function of all three of these:
mRNA: transcribed from the DNA, has the protein's composition written in it, and brings that to a ribosome where the protein will be made
tRNA: looks at the codons (set of 3 nucleotides) on the mRNA and brings amino acids which match up to that codon
rRNA: significant part of the composition of ribosomes
Now, looking at these, and back to the answer choices, we can already see that a, b, and c are correct. d, on the other hand, is incorrect. 
Hope this helps! Feel free to let me know if you have any questions about this specific problem.