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carry a rucksack
rucksack 是可数名词，指背在背部或肩上的包。
She carried a rucksack on her back.
她背上背着一个背包。
背包
先理解核心含义，再看它在真实句子里的用法。
背包
a bag carried by a strap on your back or shoulder
She carried a rucksack on her back.
她背上背着一个背包。
一种背在背部或肩部的带子包
a bag carried by a strap on your back or shoulder
She packed her rucksack with warm clothes for the weekend hike.
她把保暖衣物装进背包，准备周末去徒步。
He swung the heavy rucksack onto his shoulders before setting off.
出发前，他把沉重的背包甩到肩上。
My rucksack has a small pocket on the front for a water bottle.
我的背包前面有一个小口袋，可以放水瓶。
rucksack 是可数名词，指背在背部或肩上的包。
She carried a rucksack on her back.
她背上背着一个背包。
pack 表示把衣物、食物等装进包里。
He packed his rucksack the night before the hike.
远足前一晚，他收拾好了背包。
介词短语 with a rucksack 可用来描述随身携带背包的人。
A traveler with a rucksack asked for directions.
一位背着背包的旅行者问路。
Not this
I put my books in rucksack.
Use this
I put my books in a rucksack.
rucksack 是可数名词单数，不能裸用；前面需要限定词（如 a/the/my）。加上 a 表示“一个背包”，句子才完整。
Not this
I put my laptop on my rucksack.
Use this
I put my laptop in my rucksack.
表示“把东西放进包里”应用介词 in；on 表示“在……上面”，放在背包上意思不同。所以把 on 改为 in 才符合“装进背包”的本意。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
沉重的背包
He struggled to lift his heavy rucksack onto the shelf.
他费力地把沉重的背包举到架子上。
整理行装；打包背包
She packed her rucksack the night before the hike.
她徒步旅行前一晚就收拾好了背包。
背着背包
The soldier carried a rucksack full of supplies.
那名士兵背着一个装满补给品的背包。
徒步旅行背包；登山背包
A good hiking rucksack should fit comfortably against your back.
一个好的徒步旅行背包应该舒适合身地贴在你的背上。
背包肩带
One of my rucksack straps snapped during the climb.
我的一根背包肩带在爬山时突然断了。
Use rucksack naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
sack 就是袋子；把它背到背上，就成了 rucksack（背包）。想象远足时一个布袋绑在背上。
语域：neutral 常见场景：hiking、travel、outdoor activities rucksack 通常用于旅行、登山或户外活动场景，是比较常见的普通用词；在美式英语中不如 backpack 常用，但本身没有明显的正式或非正式色彩。
可数名词，复数形式为rucksacks。
Dictionary facts from ECDICT, WIKTIONARY, WORDNET.