He built a fire with a magnifying glass by ________ sun rays _________ the dry twigs.
A. applying, to B. exerting, on C. focusing, on D. reflecting, on正确答案C
He built a fire with a magnifying glass by ________ sun rays _________ the dry twigs.
A. applying, to B. exerting, on C. focusing, on D. reflecting, on正确答案C
