Final answer:
The life expectancy at birth during the early 1900s ranged from 30-40 years. It has since increased significantly, with the global figure being about 67 years in 2013 and higher in developed countries.
Step-by-step explanation:
Life expectancies at birth have been rising steadily since the early twentieth century. Historically, average life expectancy was between 20 to 30 years. However, this increased significantly through ecological Phase 4. As of 2013, the global life expectancy was about 67 years, and in developed countries, it was even higher. Australia, for instance, had a life expectancy at birth in 2013 of 79 years for males and 84 years for females. Considering this historical context, the correct answer to the question 'Life expectancies at birth have been rising steadily since the early 1900s when they ranged from __________ years.' is a) 30-40 years.