1
drop down
不及物用法，表示物体自身落下。
The curtain dropped down slowly.
窗帘慢慢落下。
(使)落下, 顺着向下移动
先理解核心含义，再看它在真实句子里的用法。
(使)落下, 顺着向下移动
to fall or move to a lower position
The curtain dropped down slowly.
窗帘慢慢落下。
She dropped down onto the sofa, exhausted after a long day.
漫长的一天结束后，她筋疲力尽地跌坐在沙发上。
The climber carefully dropped down from the ledge to the ground.
攀岩者小心地从岩架下降到地面。
The price of the stock dropped down sharply after the news.
消息传出后，股票价格急剧下跌。
不及物用法，表示物体自身落下。
The curtain dropped down slowly.
窗帘慢慢落下。
及物用法，表示使某物落下或向下移动。
He dropped the rope down into the well.
他把绳子放下到井里。
带介词from，表示从某处向下移动。
Water drops down from the roof.
水从屋顶滴落。
Not this
Please drop down it.
Use this
Please drop it down.
在短语动词'drop down'中，如果宾语是代词，必须放在动词和介词之间，即'drop it down'，而不是'drop down it'。这是英语中动介型短语动词的规则。
Not this
The temperature dropped down suddenly.
Use this
The temperature dropped suddenly.
动词'drop'本身就表示下降，加上'down'是多余的。在表示温度、价格等下降时，通常只用'drop'，无需再加'down'，除非特指向下移动。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
下拉菜单
Click the drop down menu to select an option.
点击下拉菜单选择一个选项。
下拉列表
Choose your country from the drop down list.
从下拉列表中选择你的国家。
下拉框
The drop down box contains several choices.
下拉框包含几个选项。
落下的窗帘
She pulled the drop down curtain to block the sunlight.
她拉下落下的窗帘以遮挡阳光。
下降到
The temperature will drop down to freezing tonight.
今晚温度将下降到冰点。
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语域：neutral 常见场景：user interface (dropdown menus)、physical descent “drop down”作为短语动词，多用于日常口语和书面语，也可用于技术语境，如描述下拉菜单或物理下落。整体比较中性。
可作及物或不及物动词使用，及物时意为‘使…落下’，不及物时意为‘落下’。
Dictionary facts from ECDICT.