. Consider the following statements

a. Both acids and bases change colour of all indicators.

b. If an indicator gives a colour change with an acid, it does not give a change with a base.

c. If an indicator changes colour with a base, it does not change colour with an acid.

d. Change of colour in an acid and a base depends on the type of the indicator.

Which of these statements are correct?

i. All four                    ii. a and b

iii. b and c                  iv. Only d