Classify the following audit procedures as (1) control risk assessment procedures, (2) tests of details of balances and transactions, or (3) analytical procedures. Give reasons for your classification.

a. Observation of a physical inventory.

b. Observation of the mail clerk opening the mail.

c. Inquiry about the client's organizational structure.

d. Inquiry about obsolete inventory.

e. Comparison of the current-year balance in an account to the prior-year balance.

f. Inspection of canceled checks for dual signatures.

g. Comparison of the recorded cost of a machine to the related vendor's invoice.

h. Inspection of sales invoices to determine if they are prenumbered.

i. Inspection of sales invoices to determine if the revenue account is properly substantiated.