Fill in the where necessary.

1. Rafflesia arnoldii is the largest flower in the world. It weighs 7kg and grows only in Sumatra, Indonesia. 2. Johann Vaaler invented the paperclip in 1899. 3. Badminton became an Olympic sport in 1992. 4. It took the Egyptians 20 years to build the Great Pyramids. 5. The most important river entering the Black Sea is the Danube. 6. The bass is the largest of the string instruments.