Some molecules are large enough ________ (see) under the electronic microscope.
to be seen
暂无解析
To succeed in a scientific research project ________.
We were busy ________ (get) things ready for the trial production when he phoned us.
The floor does not look so bad when ________ (sweep) clean.
Herefusedtotelluswhetherhe________(undertake)thejob.
heteachertoldthemsincelight________(travel)fasterthansound,lightning________(appear)togobeforethunder.
