Wemust______thattheexperimentiscontrolledasrigidlyaspossible.
A、assureI bought this eighteenth century writing desk at a quite ________ price.
EachyearintheUnitedStates,manyblackteenagers_______ofschool,eitherbecausetheycannotkeepuportheyhavetoworktosupporttheirfamily.
We must ______ that the experiment is controlled as rigidly as possible.
Each year in the United States, many black teenagers _______ of school, either because they cannot keep up or they have to work to support their family.
________theconcerthadbegundidwerealizewhatasplendidshowitwasgoingtobe.
