Which of the following processes involves changing a word by omitting certain sounds?

The correct answer is related to the process of deletion, which involves omitting certain sounds from words. In child language acquisition, deletion often occurs as children simplify complex words by dropping sounds that are less familiar or more difficult for them to articulate. For example, a child might say "nana" instead of "banana" by deleting the initial 'b' sound. This is a common phenomenon during the early stages of speech development as children gradually learn to refine their pronunciation and become more adept at producing the full range of sounds in their language.

Other processes mentioned, while they do involve changes to words, do not specifically center on the omission of sounds. Assimilation refers to the process where a sound changes to become more like a neighboring sound, thereby altering its phonetic identity rather than omitting it. Substitution involves replacing one sound with another, rather than leaving any sounds out. Consonant cluster reduction focuses on simplifying consonant clusters by dropping one or more consonants, but it doesn't specifically pertain to general sound omission across a word.