A set of numbers has the property that for any number t in the set, t + 2 is in the set. If -1 is in the set, which of the following must also be in the set?
I. 5
II. 1
III. -3
Choose the correct choice from the following options:
A) I only  B) II only  C) I and II only  D) II and III only  E) I, II, and III
The question is which of the following must be in the set, not could be in the set.   If -1 is in the set so must be   -1+2= 
<gadget id="calculator">  -1+2</gadget>
<output>1</output>
1, as 1 is in the set so must be   1+2= 
<gadget id="calculator">  1+2</gadget>
<output>3</output>
3, as 3 is in the set so must be   3+2= 
<gadget id="calculator">  3+2</gadget>
<output>5</output>
5 and so on. So basically knowing that -1 is in the set we can say that ALL odd numbers more than -1 are also in the set.   Answer: I and II only.
<result>C</result>
A set of numbers has the property that for any number t in the set, t + 2 is in the set. If -1 is in the set, which of the following must also be in the set?
I. 5
II. 1
III. -3