问题补充：
What will the world use for power when it oil?
A. run out of
B. is running out of
C. has run out
D. has run out of
答案：
A. run out of
B. is running out of
C. has run out
(答案→)D. has run out of
解析：考查词组和时态：run out和run out of，run out是不及物动词短语，没有被动式，run out of是及物动词短语，主句是一般将来时，从句用一般现在时或是现在完成时，句意：当世界用完了石油将用什么做为能源？选D。
