根据下列各句意思及所给单词的首字母或汉语提示，写出该单词的正确形式。
I hope this summer holiday will be _____________(有益的) to your study.
He was the only _____________( 目击者) of the accident, who would give important information.
Statistics _____________(表明) that the world population has doubled.
Tom was ___________(推选) chairman, for he is hardworking and responsible.
Can you _____________(推荐) a good dictionary to me ?
I wonder if you’ll c_________________ them all on their success.
She had a strong d_______ to go abroad for further study.
He was a_________ of wind in his face.
All the students p_______________ in cleaning the street.
He o________ his success to the good education he received.