<em>Remember,</em> the question is concerned about <em>"the individuals"</em> in the data set, <u>so the year they purchased their computer, neither is the amount of memory of the computer and the type of operating system can be classified as individuals in the data set.</u>
Hence, we can correctly say, only Brian's classmates are the individuals in this data set.
Opacity is the extent to which something blocks light. You can change the opacity of layers, filters, and effects so that more (or less) of the underlying image shows through.