The correct answer is: C. Either I or II is implicit.
The statement “Amongst newspapers, I always read the National Times” does not provide enough information to determine whether or not assumption I is true. It is possible that the National Times does give very comprehensive news, but it is also possible that the speaker simply prefers the National Times for other reasons. Similarly, the statement does not provide enough information to determine whether or not assumption II is true. It is possible that some people prefer other newspapers, but it is also possible that the speaker is simply unaware of other newspapers or does not have access to them. Therefore, either assumption I or assumption II could be true, but there is not enough information to determine which one is true.