are there foreign keys that I can enter in this? its a car rental company I Made up for a project but I dont know what the foreign keys are.

Table Name Primary Key Foreign Key Other Attributes Date of Sale, Time of Sale, Sale Sale No. customer number, em Amount of Sale Receipt Date, Receipt Time, Total Receive Cash Cash Rect. No. customer number, em Amount of Receipt Inventory Item No. Description, List Price Cash Acct No. Bank, Type of Account Employee Employee No. Employee Name Sales- Inventory Sale No. - Inventory No. quantity purchased, cost per unit Customer Customer No. Customer Name Services (?)