Because its is a bit more rare than iron . 
        
                    
             
        
        
        
I'll say C, Science cannot answer difficult question...let me know.
        
                    
             
        
        
        
Answer:
<h2>Genotype, sequence, mRNA, cytoplasm, proteins, phenotype</h2>
Explanation:
The allele combination at a gene locus is known as an organism's genotype, which after expression define the phenotype of that organism.
Th sequence of nucleotide in the DNA then transcribed to produce mRNA by RNA polymerase. Then mRNA exported into the cytoplasm and works as template for the  synthesis of protein. This protein defines the phenotype of that organism.
 
        
             
        
        
        
The right answer is A) Trisomy 
Aberrant karyotypes containing an abnormal number of chromosomes are known in the human species. The best-known (and most common) chromosomal abnormality is trisomy 21, which is responsible for Down syndrome (mongolism). There are others such as Turner syndrome (woman with a single X chromosome) or Klinefelter syndrome (man XXY).
These abnormalities originate from the non-disjunction of the chromosomes of a pair of homologues during metaphase I of meiosis. At the end of division I, a daughter cell contains the two chromosomes of the pair considered and the other cell does not contain a chromosome of this pair. A similar result can be obtained during a bad distribution of chromatids during anaphase II.
After fertilization from a gamete of this type, a trisomy or a monosomy is obtained.