An electronic pet flap is fitted with an RFID receiver to provide an automated security system that unlocks the pet flap as the animal approaches and locks it again once it has moved away. A unique collar worn by the pet is also fitted with an active RFID transponder. a) The active RFID transponder worn by the animal is powered by a small battery. Why might a passive system not be suitable in this instance? [1]

b) Describe the principles of operation of the RFID system in locking and unlocking the pet flap. [3]

c) Suggest a potential problem with this system.

Write a program that prints the day number of the year, given the date in the form month-day-year. for example, if the input is 1-1-2006, the day number is 1; if the input is 12-25-2006, the day number is 359. the program should check for a leap year. a year is a leap year if it is divisible by 4, but not divisible by 100. for example, 1992 and 2008 are divisible by 4, but not by 100. a year that is divisible by 100 is a leap year if it is also divisible by 400. for example, 1600 and 2000 are divisible by 400. however, 1800 is not a leap year because 1800 is not divisible by 400.