Which is the most appropriate statement?

a. Companies listed on various international stock markets are meant to subscribe to listing rules and must observe the rules.

b. Companies listed on various international stock markets are meant to subscribe to listing rules or make clear their reasons (and the implications) for failing to observe the rules.

c. Companies listed on various international stock markets are meant to subscribe to listing rules or make clear their reasons for failing to observe the rules.

d. Companies listed on various international stock markets are meant to subscribe to legal provisions or make clear their reasons (and the implications) for failing to observe the rules.