______是地球上一切生命所需的有机物、能量和氧气来源的根本保障．

根据括号中所给的汉语写出单词，使句子意思完整正确。

小题1:Though the Grade 9 students are busy with their study, they should still do sports _________ (两次) a day.

小题2:The hall is ____________ (空的). There is nobody left.

小题3:Zhang Guorong has been away for ten years. But he will be my _________(偶像) forever.

小题4:When the film ended, the audience couldn’t stop _______ (鼓掌) for a long time.

小题5:If you like to go to Hong Kong for shopping, you can go there in any ___(季节).