1 . In this question, we consider bitstrings of length $n$, where $n$ is an even integer, and in which the positions are numbered $1,2,\dots,n$.
For any even integer $n$, let $S_n$ be the number of bitstrings of length $n$ that have both of the following two properties:

• There is a 0 at every even position.
• The entire bitstring does not contain the substring 101.

Which of the following is true for all even integers $n \geq 6$?