Answer:
throughout the year, the earth tilts. This causes the north pole to be the closest to the sun half the year and the south pole to be the closest to the sun the other half. 
Explanation:
 
        
                    
             
        
        
        
Answer:
Part A: Proteins are made from amino acid monomers. There are 20 different types of amino acids which make up all the proteins of the body. The amino acids are made up of a carbon atom which is joined to an amino group, a carboxyl group and a variant group, known as R. Nucleic acids are made up of 5 carbon sugar, phosphate group and nitrogenous bases.  Hence, nucleic acids are made up of nucleotides.
Part B: Protiens are important molecule which carry out various functions of the body. They are involved in regulation of various body process. Some proteins are involved in the transportation of various molecules. Other type of proteins are involved in various immune functions and hence protect the body. For example, antibodies are proteins which defend the body against pathogens.
Nucleic acids are involved in the storing and expressing of genetic information. They also direct the body for protein synthesis.
 
        
             
        
        
        
Answer:
NAD is a coenzyme found in all cells. It consists of two nucleotides linked through their phosphate groups with a nucleotide that contains an adenosine ring and another that contains nicotinamide.
Explanation:
In metabolism, NAD participates in oxidation reduction reactions. This coenzyme is found in two forms in the cells: NAD and NADH. NAD accepts electrons from other molecules and is reduced, forming NADH, which you can use as a reducing agent to donate electrons. These electron transfer reactions are the main function of the NAD.
In living organisms, NAD can be synthesized from scratch from the amino acids tryptophan or aspartic acid. Some NADs are found in nicotinamide adenine dinucleotide phosphate (NADP), whose chemistry is similar to NAD, although it has different functions in metabolism.
 
        
             
        
        
        
Answer:
It's C. 
Explanation:
What we see as phases of the moon is the reflection of sunlight bouncing off the moon's surface.