The correct answer is but also in any approach they evolved and employed​​. Key Points​​ ​Articles are words that define a noun as specific or unspecific. The definite article 'the' is used with the name of things that are unique or already mentioned before. The article 'a' is used with the name of things that are not specific. The quantifier 'any' is also used for denoting one of the many possible options and not a specific one The article 'an' is used with the words having the first letter as a vowel and having the sound of a vowel. ​​​If a word starts with a vowel but has the sound of a consonant, it will be preceded by the article 'a'. Example: a university, a union, a one rupee note, etc. In part B of the sentence, the article 'the' will be used as a specific approach has been mentioned in the given part of the sentence. Correct Sentence: The genius of Wilbur and Orville lay not only in the singular act of getting a flying machine into the air but also in the approach they evolved and to create the technology of fight. ​​​​Additional Information ​​ Any abbreviation having the sound of a vowel will be preceded by the article 'an'. For example: He is a MLA.[ alt="false (2)" src="https://storage.googleapis.com/tb-img/production/20/08/false%20%282%29.png" style=" white-space: pre-wrap; width: 25px; height: 25px;"> He is an MLA.[ alt="right (1)" src="https://storage.googleapis.com/tb-img/production/20/08/right%20%281%29.png" style="width: 25px; height: 25px;">