Presently human population needs.................. years to double.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Population Growth**: The human population increases primarily due to a higher birth rate and a lower death rate. Factors such as improved medical facilities, education, and a better quality of life contribute to this increase.

2. **Factors Influencing Population Growth**:
- **Birth Rate**: An increase in the number of births contributes to population growth.
- **Death Rate**: A decrease in the death rate, influenced by better healthcare and education, also contributes to population growth.

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