Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
watch the video and complete the intro:

All will be handled by the controlling each . Transuranic heavy may not be used where there is . Medium weights are available: , Lead, Copper, Jet, , Radium, Sapphire, Silver and Steel. Sapphire and Steel assigned.