根据句意用下列各题空格内所给单词的适当形式填空。    

1. Robert is a Chinese Canadian. He ____      (live) in Canada for 15 years.

2. We often watch Mr Wang ____       (water) the flowers in his garden in the afternoon.

3. I'm looking forward to ___          (go) to the countryside to see my grandparents during the winter

   vacation.    

4. He decided to go for a trip in _______ (south) China.    

5. Every year, thousands of overseas Chinese students came to China to look for their _______ (family)

    roots.    

降低一个lgD值所需升高的温度，称为

A．D₀值

B．F₀值

C．D值

D．F值

E．Z值