Read the following passage and solve the questions based on it.
The only people to attend a conference were four ship captains and their first assistants. The captains were L, M, N and O; the first assistants were A, D and G. Each person in turn delivered a report as follows:
(i) Each of the first assistants delivered his report exactly after his or her captain.
(ii) The first captain to speak was M, and capta in N spoke after him.
Among the following statements which statement must be true?