OG详解-OG3 文法 Q7

Choice B is the best answer. The convention being tested is punctuation use between a main clause and a supplementary phrase. This choice correctly uses a comma to mark the boundary between the main clause (“the portraits...quilts”) and the supplementary noun phrase (“the stitching...fabric”) that provides a further description of how the portraits can be identified as quilts. 
Choice A is incorrect. A comma and the conjunction “and” can’t be used inthis way to join a main clause and a supplementary noun phrase. Choice C is incorrect because a semicolon can’t be used in this way to join a main clause and a supplementary noun phrase. Choice D is incorrect because it results in a rhetorically unacceptable sentence fragment beginning with “the stitching.”