Which of the following is an example of nominal data?

Nominal data represents categories or discrete groups that do not have a specific order or ranking. In this context, choosing tree types like Fir, Juniper, and Ponderosa exemplifies nominal data because these categories classify different types of trees without implying any hierarchy or quantitative relationship between them. Each type of tree is distinct and simply represents a different category within the broader classification of trees.

The other options represent different types of data. Temperature in Celsius is a continuous variable, which allows for a range of values and can be measured on an interval scale. The rankings of High, Medium, and Low represent ordinal data, which has an inherent order but does not measure the distance between these ranks. Lastly, speed in miles per hour is also a continuous variable that reflects a measurable quantity, which places it firmly in the realm of ratio data. Thus, the choice of tree types highlights the core characteristic of nominal data as it pertains to categorical classification.