Answer;
-A substitution frame
A form such as /_ʌt/ in which different sounds could be inserted in place of the underline is called a substitution frame.
Explanation;
-Substitution frame is a form that has a slot that can be filled in with different items. is used to identify different phonemes.
-A form such as /_ʌt/ in which different sounds could be inserted where the underline is located, is used, in part, to establish whether different sounds are different phonemes or not. A phoneme is a perceived unit of language that signals a difference in meaning when contrasted to another like itself.
-Free variation is a condition in which phonetically different sounds may occur in the same environment without changing meaning. Redundancy is when more information than necessary under ideal conditions is present.