Question

why did global human population remain relatively low up until about 1800?
up until this time, infant mortality was relatively high.
up until this time, birth rates slowly declined.
1800 is when the children of the baby boomers were themselves having children.
1800 marks the \baby boom,\ when a surge in births occurred.

Explanation:

Before 1800, limited medical knowledge, poor sanitation, and lack of reliable food supplies led to very high infant mortality. Most children did not survive to adulthood, which kept the overall population low. The other options are incorrect: birth rates were high before 1800, baby booms occurred much later (mid-20th century), so the 1800-related baby boom claims are false.

Answer:

A. Up until this time, infant mortality was relatively high.