30. Although most birds have only a negligible sense of smell, they have _____ vision.

A. vigorous B. exact C. acute D. vivid

vigorous 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