C. 
A is incorrect because if they have the disease then they cannot be healthy.
B is incorrect because if the genetic disease is recessive then the cannot have the homozygous mutated gene because then it would mean that they are ill.
D is incorrect because having an offspring that is ill doesn't always guarantee that all the offspring will be ill. <span />
        
             
        
        
        
Answer:
Option D, A subject is observed both before and after two exposures to the treatment.
Explanation:
In A-B-A-B design the alphabets have following meaning
a)	First A – It is the baseline value or the value measured before treatment
b)	First B – It is the treatment measurement
c)	Second A  - It is the withdrawal of treatment  
d)	Second B – It is the reintroduction of treatment  
The second A is known as the reversal phase in which the intervention is withdrawn to see if the target behavior returns to the baseline behaviour
Thus , there are two measurements involved one before the intervention and second after the intervention
Option D is correct
 
        
             
        
        
        
B. 6CO2 + 6H2O ------> C6H12O6 + 6O2
I hope I helped!
 
        
             
        
        
        
The answer is A. RNA polymerase will be making an mRNA using a single DNA strand as a template. So, for example if the DNA strand is AGGCAGC the mRNA strand will be UCCGUCG.
U= uracil which replaces thymine in mRNA molecules.
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i hope my answer helped!!!!!!!</span>