一朵花中，参与有性生殖最重要的结构是（　　）

    Yesterday was Sunday. Tom was at home. He got up at six o’clock in the morning. He had rice for breakfast. At eight he helped his mother do the housework. At nine he watched TV with his father. He cooked fish for lunch. At four in the afternoon he washed his clothes. He went to bed at ten in the evening.

在制作并观察人的口腔上皮细胞的临时装片的实验中，如图用具中必须要用的是（    ）

读图“漠河、北京、上海、广州四城市气温和降水分配图”，回答下列问题。

苯、甲苯是重要的芳香烃，在有机合成中有重要的广泛的用途．