下图为某国不同时期人口出生率和死亡率统计图。读图回答第下列问题。

甲时期，该国人口增长的基本特征是 （    ）

根据上下文意思，用所给单词的恰当形式完成下列短文。

        Toby came back from England yesterday. Two months ago, Toby and his classmate____(enter) a robot competition for his school. More than one hundred  ____(school) around the country joined in it, and Toby's school____(win) the first prize. As captain of his team, Toby felt very proud. He said it was a wonderful experience. But the prize sounded more fantastic. It was a holiday in England. “When the plane took off, I still  ____(do) think it was real. It was like a dream." Toby said. Someone told Toby that the first prize of the robot competition next time____(be) a holiday in America. Toby hoped to enter it then.

将用³H标记的尿苷引入某绿色植物细胞内，然后设法获得各种结构，其中最可能表现有放射性的一组结构是(　　)

— Who are they? —           .