The answer is definitely D (integral). Inseparable has a meaning like "cannot be separated from" If you use inseparable here, it means the hotels and restaurants can't be separated from the city. This use of the word inseparable is very strange in English because everyone knows that you wouldn't even try to separate hotels and restaurants from a city. What would you do with all those places ;-) ? Hopefully that helps! I am looking for students to give lessons to. Feel free to check out my profile here: https://www.italki.com/teacher/2774278

The word integral comes from integrate. To include into the city. Inseparable. Not possible to separate from each other. Has a notion of being on equal standing to a city. For example , he and she are inseparable. He and She are both people of equal entity. Integral, gears and clogs are integral parts of a watch. In your example. restaurants and hotels are minor parts of a city. They are not cities themselves.

“integral" means ”core/fundamental". It has an abstract meaning, which is why "integral part" sounds fine in [1.] but slightly unnatural in [2.] 1. Regular study is an integral part of language study 2. The monitor is an integral part of the computer Common collocates of "integral" include part, feature, aspect, role "inseparable" is quite different. It simply means "cannot be separated": 3. The couple love each other so much, they're inseparable 4. Crime and poverty are inseparable social phenomena and must be examined together I think the reason you might be confused is that both "integral" and "inseparable" have abstract meanings. For example, sentence [5.] is also unnatural-sounding (more than [2.], in my opinion) 5. "The chair is bolted to the table, therefore the table and chair are inseparable"