Wateriscomposed_______hydrogenandoxygen.
A、ofA
be composed of：由 …组成。句意：水是由氢与氧化合而成的。
It_______methreeyearstodrawthebeautifulhorses.
IsitShakespeareTheatre_______youaregoingtowatchtheplayTheMerchantofVenice?
Iftheoperation________carefullyprepared,itwouldnothavebeensuccessful.
Thetwogirlscompetedwitheachother______thehighestmark.
Thenewdiscovery_______beofgreatservicetomankind.
