Itisusefultoscience_______theearthasanobjectinspace.
A、toconsiderAftersomanydayswithoutrain,thegroundquickly________thelittlerainthatfelllastnight.
Theenginehasbrokenandtheboatis______onthewater.
Whenhesuddenly________upthesubjectofgeneticengineering,therewasanembarrassedsilence.
Shehadclearlyno________ofdoinganywork,althoughshewasverywellpaid.
Be careful, _______ you'll fall down.
