Put the Verbs in the brackets in the correct forms

1. For many years scientists (to study) the nucleus before they found that it is possible to split it.
2. Many power stations (to use) atomic energy for a long time before I knew it.
3. All this period scientists and engineers (to develop) rocket technology and electronics in close cooperation.
4. We widely (to use) electronic devices in industry for many years.
5. We know that our astronomers (to observe) the moon for a long time.
6. My friend (to make) these experiments to compare the weight of elements since the first of September
7. The question about the new experiment on this subject (to discuss) for some time before we came to a definite conclusion.
8. The fact that atom has a nucleus in its center, which is positively charged, (to discuss) by Ernest Rutherford in 1911.

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