阅读下面一首古诗，完成小题。
                                                                                                                                          雁门太守行
                                                                                                                                               李贺
                                                                                                                      黑云压城城欲摧，甲光向日金鳞开。
                                                                                                                      角声满天秋色里，塞上燕脂凝夜紫。
                                                                                                                      半卷红旗临易水，霜重鼓寒声不起。
                                                                                                                      报君黄金台上意，提携玉龙为君死。

食用油总是浮在水面上，这是因为油的密度比水 ____（小/大）；用同样的炉火给相同质量的水和食用油加热，发现水先沸腾，说明食用油的 ____比水高．