While deriving the formula for the sum of the first n terms of an arithmetic progression by pairing the first and last terms, which statement is true when n is odd?
(a) There are 2n+1 complete pairs because the middle term is counted as a pair with itself.
(b) There are 2n−1 complete pairs and one unpaired middle term.
(c) All n terms can be completely paired, giving 2n pairs even when n is odd.
(d) The pairing method works only when n is even; it cannot be applied when n is odd.