Detailed Instructions: In this task, you are given a text which is the body of a document. You are given a question and options. Pick the correct number. Don't generate anything else apart from the numbers provided in options.
Q: Context: Pseudosorghum is a genus of grass in the Poaceae family.
Question: The document can be classified to which topic? 
Options: 1)Building, 2)OfficeHolder, 3)EducationalInstitution, 4)Plant, 5)NaturalPlace
A:
4