Art historian: This painting, purportedly by Mary Cassatt, is a forgery. ... ...

Art historian: This painting, purportedly by Mary Cassatt, is a forgery. Although the canvas and other materials are consistent with most of Cassatt’s work, and the subject matter is similar to that of Cassatt’s finest paintings, the brush style of this painting is not found in any work known to be Cassatt’s. Hence this painting is definitely not a genuine Cassatt. The art historian’s argument depends on assuming which one of the following?
(A) The type of canvas and other materials that Cassatt used in most of her work were readily available to others.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Dec 2012 LSAT (PT68): Logical Reasoning B