Risk migration index is used to measure the degree of risk change of commercial banks, which is expressed as the ratio of asset quality change in the previous period to that in the current period. It is a dynamic index, so item A is correct. The amount reduced during the normal loan period at the beginning of the period refers to the loans reduced during the reporting period due to normal recovery of loans, disposal of non-performing loans or write-off of loans, so eight items are correct. The downward migration amount of interest-related loans at the beginning is the sum of the loan balances classified into subcategories, doubtful categories and loss categories at the end of the reporting period, so item C is wrong. The downward migration amount of suspicious loans at the beginning is the loan balance classified as loss at the end of the reporting period, so item D is correct.