30. Although most birds have only a negligible sense of smell, they have _____ vision. A. vigorous B. exact C. acute D. vividvigorous 精力旺盛的, 有力的, 健壮的exact 确切的, 精确的, 准确的vivid 生动的, 形象的, 鲜明的acute 敏锐的 vision 视力, 眼界