I believe the correct answer from the choices listed above is the third option. It is oxygen that is a necessary reactant for cellular respiration to occur. Cellular respiration, in a sense, is breaking down sugar in the presence of oxygen.  Hope this answers the question.
        
                    
             
        
        
        
Answer:
Thyroid gland
Explanation:
Parathyroid glands are the endocrine glands and are four in number. One superior and one inferior parathyroid glands are attached to each lateral lobe of the thyroid gland. These glands are found embedded in the tissues of the lateral lobes of the thyroid gland. During the removal of thyroid glands in patients, parathyroid glands may be mistakenly removed.
 
        
             
        
        
        
Answer:
Control of cell transition from one phase of the cell cycle to another 
Explanation:
Control of cell transition from one phase of the cell cycle to another is not the only role of cyclin in the cell. 
The role of cyclin C and H in the processes of transcription regulation is shown. 
Cyclin H, together with the transcription factor TFIIH, plays a role in the phosphorylation of the CTD-tail of RNA polymerase II during the transcription process. 
Cyclin L participates in the processes of primary transcript processing.