1. C.A works only on phonological level because phonological form can not be parapharased by anyone.

2.The source of error in strong & weak version is L1 or mother tongue, but the source of error in moderate version is L2 or target lg/we can prove moderate version in psychological of human beings .For example:the categorization of abstract & concrete patterns.

3.Word-order.subject/verb agreement,noun &noun classes, nagation,Question formation

4.As Fries said "the most effective teaching materials are thoese based on comparision of L2with L1 ;so materials were designe in a way to ensure that ,  as far as possible, learners performed without errors.Teacher should focus on different thing & explain these things more./ textbook designer same as teachers should focus on differences & designe textbook according todifferences between two lgs.

5.Richards proposed three linguistic error categories:-interference or inter lg error

-interalingual error

-developmental error:are thoes errors produce by learner at a certain developmental stage of second lg learning.