The following is on Linguistic Languages Spanish/Portuguese/English
The difference between a letter and a phoneme is:
a) Letters are symbols used to depict written words, whereas phonemes are speech sounds
b) Each letter may stand for no sound, one sound, or more than one sound, while one phoneme always stands for one sound
c) Different letters may be pronounced in the same way, but different phonemes are never pronounced in the same way
d) All of the above