When____ together, two pieces of dry wood may produce fire（）
A. rubbing
B. to rub
C. to be rubbed
D. rubbed
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____, he went to Mr. Green for help（）
A. Not to know what to do
B. To not know what to do
C. Not knowing what to do
D. Knowing not what to do
–Have you got anything ______ there？ –No, I will go there myself. Thank you just the same（）
A. to take
B. should be taken
C. to be taken
D. which should be taken
When he awoke, he found himself____ by an old woman（）
A. looked after
B. being looked after
C. be looked after
D. be looking after
This substance does not dissolve in water whether____（）
A. heating or not
B. heated or not
C. it heats or cools
D. heating or cooling
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