Comment on the specific risks $($if any$)$ that are caused by the following combination of tasks.

a$.$ A sales manager, who works on commission based on gross sales, approves credit and has the authority to write off uncollectible accounts.

b$.$ The warehouse clerk, who has custodial responsibility over inventory in the warehouse, updates the inventory subsidiary ledger and prepares an inventory summary for the general ledger department.

c$.$ The billing clerk bills customers and records sales in the sales journal.

d$.$ The shop foreman approves and submits time cards to timekerping and distributes paychecks to employees.