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an oar + verb
名词 oar 作主语，表示“一支桨”。常与 snap, break, slip 等动词搭配。
An oar snapped in the middle of the lake.
湖中央有一支桨断了。
桨
先理解核心含义，再看它在真实句子里的用法。
桨
a tool used to propel or steer a boat
An oar snapped in the middle of the lake.
湖中央有一支桨断了。
一种用于推进船只的杠杆,一端有扁平桨叶,另一端有手柄,枢于舷缘桨架上；划桨者坐于船内拉动手柄,使桨叶反复划水,利用水的阻力推动船只。
A type of lever used to propel a boat, having a flat blade at one end and a handle at the other, and pivoted in a rowlock atop the gunwale, whereby a rower seated in the boat and pulling the handle can pass the blade through the water by repeated strokes against the water's resistance, thus moving the boat.
用于推进或操纵船只的工具。
an implement used to propel or steer a boat
桨手；划桨者。
An oarsman; a rower.
多种无脊椎动物形似桨的游泳器官。
An oar-like swimming organ of various invertebrates.
He dipped the oar into the water and pulled hard.
他把桨浸入水中，然后用力划。
We need another oar to row the boat across the lake.
我们需要另一支桨才能把船划过湖。
She rested the oars on the sides of the small boat.
她把桨放在小船的两侧。
名词 oar 作主语，表示“一支桨”。常与 snap, break, slip 等动词搭配。
An oar snapped in the middle of the lake.
湖中央有一支桨断了。
此结构表示用桨作为工具来达成目的。oar 在这里是可数名词。
They used an oar to push the boat away from the dock.
他们用桨把船推离码头。
作不及物动词时，oar 常接 across, along, over 等表示方向的介词短语。
They oared across the river to reach the village.
他们划桨过河，到达村庄。
作及物动词时，oar 的宾语通常是 boat, canoe 等船只类名词。
He oared the boat into the harbor.
他划着船进入港湾。
Not this
He uses a oar to row the boat.
Use this
He uses an oar to row the boat.
oar 的发音以元音 /ɔːr/ 开头，所以不定冠词要用 an，不能用 a；这是英语中“元音音素前用 an”的规则。
Not this
There are two oar on the boat.
Use this
There are two oars on the boat.
oar 是可数名词，单数常与 a/an 搭配，two 后必须用复数形式 oars。
Not this
He paddled the boat with an oar.
Use this
He rowed the boat with an oar.
用固定在船舷上的桨划船应使用动词 row；paddle 通常指用短桨自由划动。受中文“划”的干扰，容易误用 paddle，此处应改为 row。