Final answer:
Yes, a comma is needed after the word 'knowledgeable' in the given sentence to provide clarity and avoid confusion about the professor's qualities.
Step-by-step explanation:
Yes, a comma is needed after the word 'knowledgeable' in the given sentence. The comma should be placed before the noun 'physical professor' to separate the adjective phrase 'knowledgeable' from the noun it modifies. This helps to provide clarity and avoid any confusion about the intended meaning of the sentence.
For example, the sentence could be written as: 'I have a knowledgeable, physical professor this semester.' Here, the comma helps to distinguish between the professor being knowledgeable and physical, rather than just being a knowledgeable professor of physical education.
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