If the $n$-th term of a sequence is $u_n = 1 - (-1)^n$, then — Which one of the following is true?

1. 10th term is $0$
2. 15th term is $2$
3. sum of first $12$ terms is $12$

• ai and ii
• bi and iii
• cii and iii
• di, ii and iii