(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
Converting text to lowercase is a key preprocessing step, and the reason correctly explains that it prevents the machine from treating "Hello" and "hello" as different words.
Source: Chapter 6, Section 6.5 – Text Processing (Converting Text to a Common Case)
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The textbook explicitly states: "we convert the whole text into a similar case, preferably lowercase. This ensures that the case sensitivity of the machine does not consider the same words as different just because of different cases." The Reason directly and correctly explains the Assertion, so option (A) is the right choice. In Assertion-Reason questions, always check if the Reason is a direct cause of the Assertion — here it is.