Which of the following are explicit indicators?
a. intentional obvious conclusions
b. always, never, and sometimes
c. fact and opinion
d. because, for, and since

Explicit indicators are indicators are fully and unambiguously express something and leave nothing implied, not clear.

I would need more context to be sure about how the terms above are used, but because, for, and since can play a role of explicit indicators, for example in:

Because I was hungry, I ate (the reason for eating is stated explicitly, not implicitly).

True is the correct answer

The answer to that would be prussia which would later be germany