Final answer:
Phonemic variability is the characteristic that makes English a "deep" alphabetic orthography. It means that there are many alternative spellings for the same sound, making it more difficult to predict the spelling of words based on their pronunciation.
Step-by-step explanation:
The characteristic that makes English a "deep" alphabetic orthography is phonemic variability. Unlike languages with more regular orthographies, English has many alternative spellings for the same sound, making it more difficult to predict the spelling of words based on their pronunciation. For example, the sound /s/ can be spelled with 's' in words like 'sit', 'c' in words like 'city', 'ss' in words like 'miss', or 'c' in words like 'race'.
These variations in spelling illustrate why English has a deep orthography, as opposed to languages with a shallow orthography where each phoneme typically has a single corresponding letter.