B: Blank verse
Epic poems typically have a regular meter but do not rhyme. Blank verse is metered, often in iambic pentameter, but unrhymed. A good example is John Milton's Paradise Lost.
The other options are not good choices because:
A: free verse does not have meter while epics usually do
C: rhymed verse is not common in epics - they are not rhymed
D: trochaic meter is a different meter that is much less common than iambic pentameter