Wemust______thattheexperimentiscontrolledasrigidlyaspossible.
A、assureTheproblem________whenthestudentsrefusedtodotheirhomework.
The association is ________ to raising funds to help the blind.
Thefarmerhadtowearheavybootsinthewinterbecausethefieldsweretoowetand________.
________, John has been to several foreign countries.
Senior members of the staff competed eagerly ________ the position of sales manager in the company.
