Consider the following relations for a database that keeps track of business trips of salespersons in a

Question:

Consider the following relations for a database that keeps track of business trips of salespersons in a sales office:
SALESPERSON (SSN, Name, Start_Year, Dept_No)
TRIP (SSN, From_City, To_City, Departure_Date, Return_Date, Trip_ID)
EXPENSE (Trip_ID, Account#, Amount)
Specify the foreign keys for this schema, stating any assumptions you make.