Task: Question Answering
Input (English): Question: For a certain set of numbers, if x is in the set, then x - 2 is also in the set. If the number 1 is in the set , which of the following must also be in the set ?
a) -4
b) -1
c) -5

 Option A: a only,

 Option B: b only,

 Option C: c only,

 Option D: a and b only

 Option E: b and c only
Output (English): Option D