The Earth's population has ________ since the turn of the century.

Answer: Option C

The Earth's population has Trebled since the turn of the century. It wasn't until the early 19th century that the world population reached its first big milestone: 1 billion people. Then, as the industrial revolution took hold and living standards improved, the rate of population growth increased considerably. The 20th century, however, is where population growth really took off, and over the past 100 years, the planet's population has more than tripled in size.