If $b, a, c$ are continued proportional, which combination is correct?

1. $a^2 = bc$
2. $\dfrac{a}{b-a} = \dfrac{c}{a-c}$
3. $\dfrac{a+b}{a-b} = \dfrac{c+a}{c-a}$

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