Grammar: Verbs & Tenses

1. The scientific history of radium ______ beautiful.

    was

    is

    had been

    is being

2. Radium is no more a baby but the conditions of the discovery were somewhat peculiar, and so it is always of interest ______ them and to explain them.

    in remembering

    to have remembered them

    to remember

    remember

3. Professor Curie and I worked at that time in the laboratory of the school of Physics and Chemistry where Professor Curie ______ his lectures.

    is holding

    was holding

    to hold

    held

4. All the elements ______ such radiation I have termed radioactive.

    emission

    are emitting

    have emitted

    emitting

5. I wanted ______ if there were other elements, giving out rays of the same kind.

    to know

    knowing

    know

    am knowing

6. If we ______ a practical point of view, then the most important property of the rays is the production of physiological effects on the cells of the human organism.

    are taking

    take

    takes

    to take

7. And in that way it has been proved that the radioactive elements are constantly ______ and that they produce at the end ordinary elements, principally helium and lead.

    disintegrating

    to disintegrate

    being disintegrating

    disintegrated

8. Then I ______ that there should be in the minerals some unknown element having a much greater radioactivity than uranium or thorium.

    am thinking

    think

    had thought

    thought

9. Other radioactive elements ______ since: actinium (Debierne), radiothorium and mesothorium (Hahn), ionium (Boltwood), etc.

    were discovered

    are discovered

    have been discovered

    had been discovered

10. In chemical terms radium ______ little from barium.

    is different

    differs

    differed

    is differing