B. by the sharing of electrons 
Answer choices A  and C are incorrect because covalent bonds form as a result of electrons (protons are kind of irrelevant). Answer choice D is incorrect because it describes an ionic bond. 
Further study topics: water polarity, hydrogen bonds, free radicals, valence electrons, and more! 
 
        
             
        
        
        
Answer:
The correct answer is "The emergence of a larger middle class in the North".
Explanation:
The missing options of this question are:
A) The emergence of a larger middle class in the North
B) A decline in economic inequality in urban areas
C) An increased demand for agricultural workers in the Midwest
D) The improvement of working conditions in factories
The correct answer is "The emergence of a larger middle class in the North"
The period of 1800 to 1848 is characterized by being of economical growth due to the rise in manufacturing technology. Result of this economical growth, many families improve their economical conditions and by 1848 a larger middle class emerged in the North. However, eventually a laboring poor population started to growth as well.
 
        
             
        
        
        
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❖ The homologous chromosomes (sister chromatids) move to opposite poles of the cell. The sister chromatids are pulled to opposite poles by spindle fibers.
~ ʜᴏᴘᴇ ᴛʜɪꜱ ʜᴇʟᴘꜱ! :) ♡
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Yellow because both offspring are yellow