Which phenomenon best exemplifies sound addition?

The phenomenon of sound addition refers to an instance where a sound or phoneme is added to a word, often affecting its pronunciation. In the case of "umbrella" becoming "umberella," there is an example of sound addition. The addition of the "r" sound before the "ella" modifies the original pronunciation and can reflect a phonological adjustment in the way the word is articulated, making it easier for some speakers.

In contrast, the other examples demonstrate different phonological processes. "Handbag" becoming "hambag" illustrates a sound deletion, as the "d" sound is omitted. "Strong" changing to "strung" shows a consonant transformation rather than the addition of a new sound, while "piano" becoming "piany" doesn't exemplify a straightforward sound addition but rather hints at alterations that involve vowel sounds rather than the introduction of a new phoneme. Therefore, the best example of sound addition is indeed "umbrella" becoming "umberella."