I need more explanation on each options (why options are correct or wrong)

Which of the following statements relating to the conduct of substantive tests ismost correct?

A.There is an inverse relationship between the assessed risk of material misstatement and the extent of substantive testing the auditor must perform..

B.The nature, timing and extent of substantive procedures impacts the level of detection risk achieved.

Which of the following statements relating to the use of sampling when performing substantive tests ismost correct?

C.Dollar unit sampling is an effective procedure when testing for a material misstatement in the assertion of completeness.

D.Stratification of the population allows the auditor to more effectively focus on sampling units of interest.