ANSWER
n-20
EXPLANATION
The terms of the sequence are:
-19,-18,-17,-16,-15,...
The first term of the sequence is
a=-19 and the common difference is d=-18--19=1
The rule is given by:
f(n)=a+d(n-1)
f(n)=-19+1(n-1)
f(n)=-19+n-1
f(n)=n-20.
Therefore the rule for the given sequence is n-20.
The first option is correct.
