C和D选项

问题如下：

Which of the following statements about transition matrices is incorrect?

选项：

A.Transition matrix gives probability of moving downgrade to one rating conditional on the rating at the beginning of the period only.

B.

The usual assumption of credit migration is that migrations across states are independent from one period to the next.

C.

Transition matrix shows the probability of transition from default to another rating is zero.

D.

Lower rated companies has higher probability of a rating migration.

解释：

A is correct.

考点：Credit Transition Matrices.

解析：

Transition matrix gives the probability of moving to one rating conditional on the rating at the beginning of the period， 包括持平，向上或者向下三种情况。