Explanation:

- Scientists at Cambridge University are exploring how plants can give us sustainable energy.

- Option 1: Scrutinizing

- This means examining something very closely or critically.

- This is usually associated with detailed analysis.

- It can fit, but isn’t the most common choice for research.

- Option 2: Inspecting

- This often refers to examining objects or conditions, not concepts or ideas.

- More suitable for tangible items rather than broad research.

- Option 3: Looking

- This is too vague and informal for academic research.

- Typically describes a casual or general action.

- Option 4: Investigating

- This implies systematic or formal inquiry, making it ideal for scientific research.

- It fits well with exploring new scientific hypotheses and methods.

- Answer: Investigating