Can we draw the following hypothesis from the context (see options)? 

Context:

George Booth Post (September 29, 1906 – March 26, 1997) was an American watercolorist and art educator. He was an important contributor of the California style watercolor movement (also known as the California School of watercolor) of the mid 1920s until the mid 1950s.

Hypothesis: George Booth Post has used horsehair brushes
Pick from:
 + Yes;
 + It's impossible to say;
 + No;
It's impossible to say