Which type of sampling method is being employed in the following example:

"A study was being conducted after a tsunami. The researcher was trying to assess the needs of the victims in a single
downtown high rise apartment building. So, she sent a messenger to ask one person on each floor what their needs were to
get an idea of what was needed to support the people in the building.”

Answer choice
a) Simple Random Sampling
b) Stratified Sampling
c) Clusters Sampling
d) Sampling of Convenience
e) Systematic Sampling