Final answer:
The four patentable invention classes established by Congress are Utility, Design, Plant, and Software, with software typically falling under the utility category.
Step-by-step explanation:
The correct answer to the student's question is option a) Utility, Design, Plant, and Software. In the realm of patent law, Congress has established that inventions that can be patented fall into several classes. Utility patents are for new and useful processes, machines, articles of manufacture, or compositions of matter, or improvements thereof.
Design patents cover new, original, and ornamental designs for articles of manufacture. Plant patents are granted to inventors of new varieties of plants that can be asexually reproduced. Although software as a category isn't a formal class established by Congress, software inventions can typically be covered under utility patents when they meet the criteria of being a new and useful process.