121. Local crafts people-sign, coach, and house painters-began to paint portraits as a profitable sideline; sometimes a talented man or woman who began by sketching family members gained a local reputation and was besieged with requests for portraits; artists found it worth their while to pack their paints, canvases, and brushes and to travel the countryside, often combining house decorating with portrait painting. The word "sketching" is closest in meaning to which of following?
解析：