CORRECT answer is option 4) i.e. kept. The PASSAGE is all about "The Human Body."From the last sentence of the passage "About a gallon of it is in the blood vessels and is (5) circulating by temperature", we can say that it is discussed how the water keeps circulating in the human body.In "is (5) circulating by temperature", the option 'kept ' is best suitable to be fitted in the blank.Hence, the option 'kept' is contextually correct. Read thoroughly: Read the passage thoroughly to get an idea of the passage. Read slowly and gain an understanding of the text. Once the theme of the paragraph is clear, it becomes easy to fill in the blanks.Type of word to fill in: Look at the blanks carefully and try to assess which kind of word to put in the blank. Words can be based on grammar, prepositions, TENSES, vocabulary etc.Tone: Passage may contain some specific tone like narrative, critical, sarcastic, humorous etc. So, always make the right choice of a word.Negate options: Sometimes, words are too close, eliminating wrong choices can help.Link the sentences together: Always remember, it is a passage, so the sentences are linked to one another. Never make a mistake of treating every sentence an individual one.KEYWORDS: PAY close attention to keywords/ clues in the sentences before and after the given blank.