Explanation
Correct answer: A.
Choice A is the best answer. The convention being tested is the use of punctuation between titles and proper nouns. No punctuation is needed between the proper noun “Yugang Sun” and the title that describes Sun, “chemistry professor.” Furthermore, no punctuation is needed after “Sun” because “chemistry professor Yugang Sun and his colleagues at Temple University” functions as the coordinated subject of the sentence, and together Sun and colleagues performed the action of developing a new approach to producing iron nanoparticles.
Why the other choices are wrong
Choice B
Choice B is incorrect because no punctuation is needed between the proper noun “Yugang Sun” and the coordinated noun phrase “and his colleagues at Temple University.”
Choice C
Choice C is incorrect because no punctuation is needed before or after the proper noun “Yugang Sun.” Setting off the professor’s name with commas suggests that it could be removed without affecting the coherence of the sentence, which isn’t the case.
Choice D
Choice D is incorrect because no punctuation is needed between the title “chemistry professor” and the proper noun “Yugang Sun.”