If you <u>belong to a group of people</u>, you are a <u>member of that group</u> and you are considered part of it. An excellent example is being a member of a Club or translated to Spanish:
<h2>Ser miembro de un Club
</h2>
Therefore, the right answer is D.
The other options, such as:
<em>-Saber</em> (to know)
<em>-Jugar Videojuegos</em> (Playing video games)
<em>-Hacer una búsqueda</em> (to search)
Do not necessarily involve belonging to a group of people.