Answer:
C
Explanation:
the fibrin definition tells us that the first term of the sequence a1 = 6
so, B is out.
and for every following term we always add 7 to every previous term to create the next one.
so, when I add 7 to 6, what is my second term in the sequence ? 7+6 = 13
not 42, not -7
therefore, only C is correct.
and 13+7 = 20
and 20+7 = 27
it all fits