Final answer:
The shortened form of the 7-letter word that "chat" comes from is 'chatter'. Various spellings of the [ch] sound exist in English, such as , , and , with 'yacht' being a unique case of [t] spelled due to historical changes in language.
Step-by-step explanation:
The word "chat" is indeed a shortened form of the word chatter, which is a 7-letter word. Therefore, the correct answer from the options given is a) Chatter. In English, there are various ways in which the sound [ch] can be spelled, including , , and . For example, we can find this in words like chalk and watch, where the sound is straightforward, and in words like questioner and adventurous, where the [ch] sound comes from a followed by an unstressed u.
A unique case is the word yacht, which is the only English word in which the sound [t] is spelled . This spelling has evolved from the Dutch word "jaghte", indicating how language and spelling can change over time. Additionally, Italian and German provide examples of other spellings for the [ch] sound, such as cello and kitsch, where it is spelled and , respectively.