Explanation:

- Air Purifiers: These devices are designed to filter and clean indoor air pollution but are not relevant for reducing crude oil imports. They do not serve as an alternative energy source.

- Biofuels: These are renewable fuels derived from biological materials. Biofuels are the correct answer as they can serve as an alternative to fossil fuels, thus helping to reduce crude oil imports. Additionally, they produce fewer emissions compared to conventional petroleum fuels, potentially mitigating pollution.

- Extractor Fans: These are used for ventilating indoor spaces by removing pollutants or moisture but have no direct connection to crude oil import reduction or addressing large-scale environmental pollution.

- Phytoremediation: This is a process using plants to remove contaminants from the environment. While beneficial for cleaning soil and water, it does not provide an alternative to fossil fuels or reduce crude oil imports.

Correct Answer: Biofuels