试题题干
The paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Choose the missing words of the phrase or sentence.
All plants and animals that have been studied carefully (including humans) seem to have build-in clocks. They know the time naturally and correctly without any help from outside.
To have a （） clock.
参考答案
正确答案：
试题解析
大意：拥有一个生物钟。biological clock生物钟。