_______ difficulty we meet with, we must finish it on time, because the opportunity is _______ valuable.

In Copenhagen Climate Conference，rich countries promised to________a fund of $100 billion a year by 2020 to help developing countries.[ ]

I’ll go to Hong Kong for a trip next weekend. — Great! _______

To be able to catch up with the other students, he needs ___ hard work; he needs your encouragement, too.

Can I use your pen ______ is broken.-Sure.