1. At present, more than one million visitors travel to Guangzhou every year.
2. Their relationship was based on/ upon years of open communication with each other.
3. The world’s fresh water resources are very limited so we must make good use of them.
4. I will gladly take part in any discussion that enriches my knowledge of the world.
5. Believe it or not, we have gradually become able to express ourselves fluently in.