Here are the suggested answers for the numbered blanks in the passage:

1. A. music
2. C. musical
3. A. number
4. D. located
5. C. recommend

So, the completed passage would read:

Donauinselfest is the largest free outdoor (1) **music** festival in Europe. It is a festival which takes place on Danube Island in Vienna, Austria. In the first year, 160,000 people attended, and the festival lasted one day. Nowadays, the festival lasts three days. What makes the festival so good is the (2) **musical** of music and quantity of acts. It has twelve stages, and on each stage a different (3) **number** of music is played. Over the three days, more than 300 music, theatre and cabaret acts perform. There is also a competition called ‘Rock the Island Contest’ where new bands and artists can compete for a chance to perform at Donauinselfest. Each year over 500 bands and artists enter the competition!

Another good thing about the Donauinselfest is that it is (4) **located** on an island. The island has lots of greenery and you can see the beautiful Danube River. Despite being located on an island, it is very easy to get to Donauinselfest. The island has two underground train stations, both of which connect to central Vienna. Next year Donauinselfest runs from 23rd - 25th June. I highly recommend (5) **recommend** it!