Solution
✅ Correct Option: 1
Option 1: has only been conducted using specific plants.
The passage tells us that the research was carried out using certain selected plants — scientists picked particular types of plants to experiment with rather than testing every plant in the world.
Why the other options are wrong:
- Option 2 → The passage does not limit the research to just NASA; other scientists may have also been involved.
- Option 3 → The passage does not say that researchers failed to identify where the chemical impurities come from.
- Option 4 → The research has benefits beyond just long-term space exploration — it can also help people on Earth, such as by improving indoor air quality.