The correct answer is option D, difficulty of redesigning workable ecosystems
Reason - 
The area that was redesigned into an ecosystem actually failed to attract the endangered species of clapper rails in California because of the following two reasons –
a)	Failed attempt of restoration of Cord grass ( a tree which is a dominant tree in the nesting habitat of clapper rail) . Even if few such trees were there they could not grow to their full height and thus were incapable of providing adequate nesting cover
b)	Due to the lack of predatory insect, some herbivore insect in the ecosystem attacked the green grasses thereby making the nesting inadequate.
 
        
             
        
        
        
Answer:
C. Both (a) and (b) 
Explanation:
Hunting, destroying habitats, polluting and introducing non-native species can cause extinction. 
 
        
                    
             
        
        
        
I'm pretty sure the answer is B
        
             
        
        
        
The correct answer to the question which is stated above is obviously the first option: <span>the Moon has very little atmosphere
</span>The climate on the Moon is harsh because  the Moon has very little atmosphere. The moon can never<span> be too close or too far because it is right next to earth. </span>
        
                    
             
        
        
        
Answer:
Explanation:
A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated into the host’s genome by an integrase enzyme. The virus thereafter replicates as part of the host cell’s DNA. Retroviruses are enveloped viruses that belong to the viral family Retroviridae. A special variant of retroviruses are endogenous retroviruses, which are integrated into the genome of the host and inherited across generations. Endogenous retroviruses are a type of transposon.