As a rule, \u201Can\u201D should only be used before words that start with a vowel (i.e. a, e, i, o, and u) or before a word that contains an unpronounced \u201Ch\u201D (i.e. hour). Therefore, \u201Ca\u201D should be used before words that begin with a consonant (i.e. b, c, d, f, ...). In this sentence, the next word after \u201Can\u201D starts with a consonant; therefore, \u201Ca\u201D should be used. \u201CThrough\u201D and \u201Cthru\u201D can be used interchangeably; therefore, it would not correct the sentence to change one to the other. Using \u201Creproduced\u201D would create a parallelism error. The sentence is only talking about one process (\u201Cmitosis\u201D); therefore, you should not change the singular form of \u201Cprocess\u201D to the plural form.