“However,” 在这里只是一个引导性的副词，这个句子就是有意义了。

Once it's clear that "however" is just an introductory adverb, the sentence makes sense.

youdao

句子主干是itwillpassthroughsharpmetalbars。第一个which引导的定语从句修饰的是sharp metal bars。

First it will pass through sharp metal bars which will tear open the plastic bags in which rubbish is usually packed.

youdao

从句不是一个句子，通常由引导词引导。

A dependent clause cannot be a sentence. Often a dependent clause is marked by a dependent marker word.

youdao

从句不是一个句子，通常由引导词引导。

A dependent clause cannot be a sentence. Often a dependent clause is marked by a dependent marker word.

youdao