1． Barack Obama, ______ president of the USA, and Mitt Romney started on Monday night to
debate on ______ foreign policy in their third and final face-to-face argument.
A. /, the B. the, / C. /, / D. the, the
2. Make sure ______ the experiment is over, all the electric facilities in the lab are turned off.
A. that once B. if once C. once if D. once whether
