移民加拿大..help help

I send my file Nov.17.03, they return all the file yesterday, the reson is
They ask a official language test or a letter from me
explanation how good my English is,
Is any body know they reqired test or explanation letter? because I already have a Master's degree in US(I am LZ take a language test)
Is does, Is anyone have a sample letter or how i find
a sample letter. [e-mail]

Thank you so much