The correct option is A Alteration
The meaning of the underlined verb 'alter' is: to make changes to.
The verb must be replaced with a noun, because the word before it, 'need', is a verb. A verb is generally followed by a noun. (It is sometimes followed by an adverb when it modifies the verb.)
Option B: From the options, 'alteration' is the most suitable word, as it's a noun.
It refers to 'the process of altering'. Hence option B is correct.
Option A: 'Altered' is a verb or an adjective, depending on its usage. As a verb, it cannot be placed after the verb 'need'. As an adjective, it cannot be used as there's no noun after it which it can modify.
Option C: 'Alternating' is a verb. Also, it has a different meaning from 'alter'. It means 'to occur in turn repeatedly'.
Option D: Similarly, 'alternate' is also a verb. It does not complete the sentence in meaning.
Hence options A, C and D are incorrect.