Which country is made up of 176 islands, 36 of them inhabited, in 3 groups (called Vava'u, Ha'apai, and Tongatapu) which stretch north-south for 800 kilometers (500 miles)?
What is the name for the highly viscous layer of the earth that is about 2,890 km (1,800 miles) thick and makes up about 84 percent of Earth's volume?
