------- living in the water, whales breath air. ?

In the sentence “------- living in the water, whales breathe air,” we need a word that introduces a contrast between two facts: whales spend their entire lives in water, yet they must surface to inhale oxygen. The correct choice is the preposition “Despite.” Here’s why:

1. Function of “Despite”
- “Despite” is used to show contrast or concession and is always followed by a noun, pronoun or gerund (–ing form).
- In our sentence, “living in the water” is a gerund phrase, so it slots perfectly after “Despite.”

2. Why the other words don’t work as well
- “Though” is a conjunction that introduces a full clause (subject + verb). You could say “Though they live in the water, whales breathe air,” but you cannot directly follow “Though” with just a gerund phrase.
- “For” functions as a preposition meaning “because,” which would reverse the logic (it would imply “because they live in the water, whales breathe air,” which is illogical).
- “Now” is an adverb of time and has no concessive meaning, so it does not express any contrast.

3. Comparison with similar structures
- You could also write “In spite of living in the water, whales breathe air.” “In spite of” is a synonym of “Despite,” but it’s longer.
- Both “Despite” and “In spite of” carry the same sense of “even though” when introducing a noun or gerund.

4. Putting it all together
- Correct sentence: “Despite living in the water, whales breathe air.”
- This clearly shows that even though whales’ habitat is aquatic, they take in atmospheric oxygen.

Summary
• “Despite” introduces a contrast and takes a gerund or noun.
• Other options fail to convey the right meaning or grammatical structure.
• The sentence correctly highlights the surprising fact about whales’ need to surface for air.