Find the General Term of the Arithmetic Sequence Then Find $a _ { n }$

Multiple Choice

Find the general term of the arithmetic sequence then find the indicated term of the sequence. Assume that the domain of the sequence is all natural numbers.
-Find $a _ { n }$ and $a _ { 18 }$ .

A) $a _ { n } = n - 4 ; a _ { 18 } = 14$
B) $a _ { n } = n + 4 ; a _ { 18 } = 23$
C) $a _ { n } = n + 3 ; a _ { 18 } = 21$
D) $a _ { n } = n - 3 ; a _ { 18 } = 15$