Li Bang, a credit manager for a medium$-$sized commercial business, hears lots of reasons from customers for not paying their bills. He needs to distinguish between excuses indicating that payment will be made eventually and definite causes indicating that payment may never be made. Upon hearing which of the following should Li conclude that a customer really cannot pay?

a$.$ "The check is in the mail."

b$.$ "There's a glitch in our accounts payable software."

c$.$ "We're having a cash flow problem."

d$.$ "We've filed for Chapter $11."$