南水北调工程的实施，对我国华北地区有百利而无一害。（    ）（判断对错）

①将体积相同的铝合金和泡沫塑料块分别放在天平的左右盘内，会观察到天平不平衡．表明：体积相同的不同物质，____．

②将体积大小不同的两块泡沫塑料块分别放在天平的左右盘内，同样会观察到天平不平衡．表明：____，体积不同，质量不相等．

③选取体积不同铝合金进行定量实验，实验数据如表．

a．分析比较表格中的实验数据，可以初步得出结论：____．

b．为了得到比较完整的物质质量与体积的定量关系，还需要进一步实验，进一步实验设计方案是：____．

选择合适的关联词语填空。

因为……所以……与其……不如……虽然……但是…．

不是……就是……不但……而且……宁可……也不…．

①____前进的道路上还有困难，____我们一定能够克服。

②老师常常告诉我们，____考试前加班划线搞突击，____平时刻苦学习。

③王平____诚恳地接受了批评，____坚决地改正了错误。

④邱少云____牺牲自己，____挪动一寸地方。

    Have you ever heard an echo of your voice?
    An echo is a reflected(反射)sound. Stand in a very large, empty hall with nothing on the walls. Then shout. The sounds you make will hit the walls and come back to you. The walls reflect the sounds. These reflected sounds are called “echoes”.
    We can use reflected sound to make sound travel farther. Hold a watch about fifty centimeters from your ear. You cannot hear it. The sound of the watch travels a short way in all directions. It does not travel as far as your ear. You can make it travel to your ear by using a roll of cardboard(纸板筒).
    Make the roll of cardboard about fifty centimeters long. Put one end over your ear and hold the watch at the other. Now you can hear the watch because the sound has not gone in all directions. It is reflected down the roll to your ear.
    A megaphone(喇叭筒)works in the same way. It makes sound travel farther. It reflects the sound into a beam which can travel a long way. In the ship, the sailor uses the megaphone to make his voice travel. Without the megaphone, his voice cannot travel far.
    We use reflected sound in many ways. We use it to measure the depth of the sea, for example. Among the animals, bats and whales use reflected sound to tell them where they are and what things are near them.