30. Although most birds have only a negligible sense of smell, they have _____ vision.
A. vigorous B. exact C. acute D. vivid

<vigorous>
vigorous 精力旺盛的, 有力的, 健壮的
</vigorous>

<exact>
exact 确切的, 精确的, 准确的
</exact>

<vivid>
vivid 生动的, 形象的, 鲜明的
</vivid>

<acute>
acute 敏锐的
</acute>

<vision>
vision 视力, 眼界
</vision>