Itisusefultoscience_______theearthasanobjectinspace.
A、toconsiderHethoroughlyunderstoodthesociety__________.
Asyoulikepopmusic,__________Ilikeliterature.
Theenginehasbrokenandtheboatis______onthewater.
________withthesizeofthewholeearth,thehighestmountainsdonotseemhighatall.
Wemust______thattheexperimentiscontrolledasrigidlyaspossible.
