Exponential phase of human population started in........

Explanation

**Step-by-Step Solution:**

1. **Understanding Population Growth Phases**: The human population growth can be divided into different phases, including the stationary phase and the exponential phase. The stationary phase is characterized by a stable population size with little to no growth.

2. **Identifying the Stationary Phase**: Before 1750, the human population was relatively low, estimated to be around 300 million. During this time, the population growth was minimal, indicating a stationary phase.

3. **Recognizing the Start of Exponential Growth**: The exponential phase of human population growth began after 1750. This is when the population started to increase rapidly due to various factors such as advancements in medicine, agriculture, and sanitation.

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