Part D. E-R Mapping (28 points, 7 points each). Below is an E-R diagram that conceptualizes the business requirements for a cab company. Consider this diagram for questions 1821. Select all answers that apply to each multiple-choice question. Some questions may have multiple answers. Consider the assigned relationship between DRIVER and CAB. Which of the following is true if NULLs must be avoided? a. Store DriverID as the foreign key in the CAB relation, and store the CarID as the foreign key in the DRIVER relation. b. Store the CarID as the foreign key in the DRIVER relation. c. Store DriverID as the foreign key in the CAB relation. d. It is not possible to avoid NULLs in this instance. e. NULLs cannot be avoided unless a new relation is created