Portia，for ________ physics had once been very hard，turned out to be a physicist.

(2009·陕西)Gun control is a subject ________ Americans have argued for a long time.

(2010·上海)Wind power is an ancient source of energy ________ we may return in the near future.

She showed the visitors around the museum，the construction ________ had taken more than three years.(2011·江西)

Julie was good at German，French and Russian，all of ________ she spoke fluently.(2011·湖南)

Care of the soul is a gradual process ________ even the small details of life should be considered.(2012·湖南)

The man showed us such a heavy stone ________ no one could lift it.

Can you lend me the book ________ the other day?

At the party，John made up a joke，________ people burst out laughing.

That is the day ________ I'll never forget.