Final answer:
The phonological process that removes unstressed syllables from words to shorten them is known as Unstressed Syllable Deletion, often seen in children's language development.
Step-by-step explanation:
The phonological process that involves the removal of unstressed syllables from a word to create a simplified or shorter form is c) Unstressed Syllable Deletion. This process is often observed in language development in children, where they may simplify a multisyllabic word by dropping an unstressed syllable. For example, a child might say 'nana' instead of 'banana'. The other options listed, such as reduplication, involve the repetition of sounds or syllables; postvocalic devoicing refers to the devoicing of voiced consonants at the end of words; and morphological assimilation is concerned with changes that happen to a morpheme when it is combined with other morphemes.