是平行四边形,把△ABD沿对角线BD翻折180°得到△
.
.(要求保留作图痕迹,不写作法);
与BC交于点E,求证:△
≌△
.
,则“
”是“
”的( )
①乡村规划应坚持绿色发展,提高村民幸福指数
②以美丽乡村建设为工作中心,改善乡村环境
③加强不同地区的区域合作,有助于互利共赢
④既要扬长避短,因地制宜,又要加强区域联系
:氧化镁中镁原子的化合价为+2价
C . 2Al:两个铝原子
D . N2:一个氮气分子中含有两个氮原子

In northern Scotland there is a long, deep lake called Loch Ness. More than 200 meters deep, it is the largest lake in the UK.People say a big monster lives in its dark, cold waters. It weighs more than 1,000 kilos and is at least ten meters long. Some people say it has a head like a horse. Others say it looks 1ike a snake. Many people travel to Loch Ness to look for this strange monster, but only a few people have seen it. At least, they say they have seen it.
Loch Ness Monster is a famous legend. The first story about a monster in Loch Ness was told over 500 years ago, but the legend of the monster spread widely only in the twentieth century. In 1933, a husband and wife reported that they saw a big monster in the middle of the lake. Since then, a number of people have said that they have seen a monster in Loch Ness. Several people have taken photos, but at least one of them was a hoax. During the 1960s, a team was formed to look for the monster. They took many photos and made movies, but they were never able to find a monster.
There is no real fact that a monster lives in Loch Ness, but there is also no fact that one doesn't live.One thing is true about Loch Ness : there are a lot of tourists there.
材料一:左图是北京市铁路网图,右图北京市气温曲线图和降水量柱状图

材料二:北京是全国高等院校最集中的地区,有众多的体育场馆,博物馆,中央电视台和中央人民广播电台,以及许多国家级的文艺团体等。
材料三:北京是一个重度缺水的城市,水资源人均占有量为300立方米左右,仅为全国人均占有量的七分之一,在世界各国首都中居百位之后,现在北京主要供水源地密云水库的来水量日益减少。
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wēi xiǎn |
yǎng wàng |
yǎn zòu |
xīn shǎng |
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fēng fù |
guān chá |
luó bo |
xiān yàn |
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物质 |
实验实数 |
体积/ | 质量/ | |
| 甲 | 1 | 10 | 9 | 0.9 |
| 2 | 20 | 18 | 0.9 | |
| 3 | 30 | 27 | 0.9 | |
| 乙 | 4 | 10 | 27 | 2.7 |
| 5 | 20 | 54 | 2.7 | |
| 6 | 20 | 81 | 2.7 |
①
×
÷ 
②2.4÷
+6.4
③
+
÷ 
④(
+
)×12
⑤(
-
)÷(
+
)
⑥
×
+
÷ 