allophonic rules... please help at all?

[naomijade]

hi,
i am reading on allophonic rules at the moment and there is a quiz inside it after the chapter. i am so confused because i have been racking my brain about this exercise and i have re-read the chapter over and over. any help at all, please? the exercise is below.

Vowel length in English is an example of allophonic variation. Vowels often have the same quality but are different in length. Work out the rule that produces this allophonic variation.

there are a few word examples but i can't use IPA here. a few of the word examples of the variations are from words such as: root, tar, runs, pass, peck and treat.

:s :s so confused!

[Tdol]

Read this for IPA symbols: http://www.usingenglish.com/forum/pr...c-symbols.html