Which of the following is true regarding the relationship between tests of controls and procedures to obtain an understanding?
选项：

A:In obtaining an understanding of internal control, the procedures to obtain an understanding are applied to all controls identified during that phase.;
B:Tests of controls are applied only when the assessed control risk has not been satisfied by the procedures to obtain an understanding.;
C:Procedures to obtain an understanding are performed only on one or a few transactions.;
D:All of the above are correct.