The correct option is B teeming
The sentence "(Kolkata) It is always ___ with people..." requires a word that can describe the city, Kolkata.
Option B: 'Teeming' is an adjective that means 'to be full of or swarming with'. The meaning is apt for the given sentence, as it means that Kolkata is always filled/crowded with people during the day as well as night.
Hence option B is correct.
Option A: 'Moving' is used for a person or object that can position from one place to another. For example, a moving van. It cannot describe a city (Kolkata is moving) as cities are immovable. Hence A is incorrect.
Option C: 'Seeking' refers to an attempt to find something, look for something. It's a verb and does not describe a city. Hence C is incorrect.
Option D: 'Thriving' means 'growing and flourishing'. It refers to progress and prosperity, but not in the context of this sentence. This is because 'it is always thriving... day and night' does not relate to Kolkata being a busy city.
Hence option D is incorrect.