| Questions | Answers |
|---|---|
| The gas we breathe in | oxygen |
| the apparatus worked on the principal of reflection | periscope |
| the apparatus worked on the principal of reflection | periscope |
| the apparatus worked on the principal of reflection | periscope |
| The gas we breathe in | oxygen |
| the apparatus worked on the principal of reflection | periscope |
| The gas we breathe in | oxygen |