Exempt from Income Tax

Hi, on ACCA BPP “Taxation UK” revision kit for FA 2017, there is a question:

– Which TWO of the following types of income are exempt from income tax?
a- Interest on an NS&I Investment account
b- Premium bond prizes
c- Interest on UK government stocks (‘gilts’)
d- Dividends on shares held in an Individual Savings Account

And the answer on the same book is:
The two right choices are:
-Interest on an NS&I Investment account
-Interest on UK government stocks (‘gilts’).
Premium bond prizes and dividends on shares held in an Individual Savings Account are exempt.

Looks to me like it states the same thing for all of them. Can you explain what the answer means? Thanks in advance