OG详解-OG2 文法 Q18

Choice D is the best answer. The convention being tested is punctuation use between two supplementary phrases following the coordinate clause (“but she…mycology”). This choice correctly uses a comma to mark the boundary between the supplementary noun phrase (“the study of fungi”) that defines the term “mycology” and the supplementary participial phrase (“producing...London”) that provides additional information about the extent to which Potter dedicated herself to mycology. 
Choice A is incorrect because a semicolon can’t be used in this way to join two supplementary phrases following a coordinate clause. Choice B is incorrect because it results in a rhetorically unacceptable sentence fragment beginning with “producing.” Choice C is incorrect. The lack of punctuation results in asentence that illogically suggests that the study of fungi is producing more than 350 paintings.