Here are the appropriate answers for the blanks in the passage:

21. A. full
22. A. amenities
23. A. travel
24. B. but
25. A. excitement

So the complete passage would read:

Life in the concrete jungle of downtown can be both exciting and challenging. The roads are often congested, (21) **full** with cars, buses, motorbikes and bicycles. The city is bustling with a variety of activities, from early morning to late at night. There are many public (22) **amenities** like parks, libraries, shopping centres and restaurants but these places are often full of people. Sometimes pickpockets are a problem. This is a part of city life that we should be careful about.
To escape the traffic jams, many city dwellers (23) **travel** the sky train or underground metro. These public transport systems provide a quick and efficient way to get around the city. Living in the city can be crazy sometimes (24) **but** many people still love it. In fact, lots of people from quieter places even choose to move here. They love the (25) **excitement** and feel like there are more chances to make their dreams come true in the city.