A good index fossil is one with four characteristics: it is distinctive, widespread, abundant, and limited in geologic time. Because most fossil-bearing rocks formed in the ocean, the major index fossils are marine organisms
        
             
        
        
        
They both contain a Nucleus, the part of the cell designed to dictate the cells operations.
        
             
        
        
        
Answer:
a) HT
Explanation:
This question shows an animal with two distinct unlinked genes i.e. on different chromosomes. One gene codes for head shape and the other for tail length. The gene for head shape possess alleles H and h, while gene for tail length possess alleles T and t. 
According to Mendel's law of independent assortment, the alleles of a gene will separate into gametes independently of the alleles of another gene. This occurs in such a way that each gamete will contain only one allele from a gene.
Based on this principle, an animal with genotype HhTt will undergo meiosis and randomly produce gametes with the following allelic combinations: HT, Ht, hT, and ht. As seen in the gametes, only one allele of a gene occured in a gamete at a time. 
Therefore, HT is the genotype possible in a gamete of parent: HhTt.
 
        
             
        
        
        
Answer: El Niño is a part of a routine climate pattern that occurs when sea surface temperatures in the tropical Pacific Ocean rise to above-normal levels for an extended period of time.
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<em>hope this helps !_!</em>
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ENJOY groovie DAY</u></h2>