______ WE CAN FIND OUT NEW SOURCE OF ENERGY, OUR LIFE WILL CERTAINL...

7. - 30 BAI TRAC NGHIEM VOI KEYS FOR 9 P
30 BAI TRAC NGHIEM VOI KEYS FOR 9 P

7. ______ we can find out new source of energy, our life will certainly be destroyed.

C. its C. the

A. if B. when

C. unless D. even though