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 service relationship between CAB and MECHANIC. Which of the following is true? a. CarID can be stored in MECHANIC as a foreign key. NULLs are not possible. b. Phone can be stored in CAB as a foreign key. NULLs are possible. c. A new relation must be created to represent this relationship. d. CarID can be stored in MECHANIC as a foreign key. NULLs are possible. e. Phone can be stored in CAB as a foreign key. NULLs are not possible. Consider the parks relationship between CAB and GARAGE. Which of the following is true? a. A new relation must be created to represent this relationship. b. Address can be stored in CAB as a foreign key. NULLs are possible. c. CarID can be stored in GARAGE as a foreign key. NULLs are possible. d. Address can be stored in CAB as a foreign key. NULLs are not possible. e. CarID can be stored in GARAGE as a foreign key. NULLs are not possible