单选题 .  ①Unlike the static, classically composed portraits produced by her mentor Walker Evans, twentieth-century New York photographer Helen Levitt's photographs seem candid and spontaneous. ②Whereas Evans' subjects look directly into the camera, so that photographer and subject conspire in the making of a portrait, Levitt's subjects seem caught unawares. ③As a "street" photographer, before the term's invention, Levitt has claimed to have attempted to capture life as she found it. ④But there is a paradox to her technique. ⑤Her off-the-cuff aesthetic seemingly guarantees objectivity, since she was recording street scenes she happened upon, yet her photographs could be said to be highly subjective, to be reflections of Levitt's own distinctive preoccupations and ways of seeing. ⑥Unlike Evans' images, Levitt's are solely the products of the photographer without the conscious participation of their subjects. ⑦The repetitions evident in Levitt's choices of subjects, for example her many photographs of children in masks and disguises, reveal more about Levitt herself than about those subjects.3.  According to the passage, which of the following appears to ensure the objectivity of Levitt's photographs? ______