Itisusefultoscience_______theearthasanobjectinspace.
A、toconsider________they'vegottoknoweachotheralittlebetter,theygetalongjustfine.
For the new country to survive, ________ for its people to enjoy prosperity, new economic policies will be required.
Becareful,_______you'llfalldown.
The problem ________ when the students refused to do their homework.
________ the concert had begun did we realize what a splendid show it was going to be.
