第16题: [多项选择]Definition: Optimal forage means some animals try to waste as little energy as possible to obtain food 参考答案:A kind of birds that prey on shellfish, they swoop down from sky to catch the shellfish in the water,then fly to a certain height and drop the shellfish on rocks for them to crack open, the birds choose to drop the biggest shellfish every time to obtain the highest energy, also they fly up to E meters high to drop the shellfish. It’s neither too high for the birds to waste energy, nor too low for the shellfish not to crack open.
第24题: [单项选择]Ever since the family moved to the suburbs last year, they ______ better health. A. could have enjoyed B. had enjoyed C. have been enjoying D. are enjoying 参考答案:C 答案解析:本题考时态。根据句意确定该句应用现在完成时态。本句大意为：这家人自从去年搬到郊区以来，健康状况好多了。
