Consider the following statements about 2's complement: Which of the following is correct?

1. 2's complement removes the problem of having both $+0$ and $-0$
2. To get the 2's complement, add 1 to the 1's complement
3. If the MSB is 1, the number is positive

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