Write the factors that have led to decline in the death rate.

Explanation

### Step-by-Step Solution:

1. **Introduction to Population Growth**:
- The human population has experienced explosive growth over the last century, increasing from approximately 2 billion in 1900 to around 6 billion by the year 2000.

2. **Decline in Death Rate**:
- The significant decline in the death rate (or mortality) is a primary factor contributing to this rapid population growth.

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