Art critic: Abstract paintings are nonrepresentational, and so the only measure of their worth is their interplay of color, texture, and form. But for a painting to spur the viewer to political action, instances of social injustice must be not only represented, but also clearly comprehensible as such. Ttherefore, abstract painting can never be a politically significant art form. Which one of the following is an assumption that is required by the art critic's argument? ['Paintings that fail to move a viewer to political action cannot be politically significant.', 'The interplay of color, texture, and form is not a measure of the worth of representational paintings.', 'Unless people view representations of social injustice, their political activity is insignificant.', 'Abstract painting cannot stimulate people to act.']