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>