國內教英文，喜歡把by which, for which, in which等等看做組合來教。其實並不是什麽固定用法，只不過這句裏面有which，又恰好應該用by而已。（by有很多固定搭配，但是by which作為壹個固定搭配來查，在美林韋氏詞典裏都查不到）
這句話之所以是by，是因為句子主體結構的原因。理解句子的最好的辦法是縮句。我把非主體的單詞略去，簡化後就很清晰了：The process by acquiring is important。acquiring就是“a society acquires capital equipment”這部分，雖然長，但是當作壹個名詞就可以了，為了結構清晰我用acquiring來替代。which在這裏指process，相當於強調，沒有實際意義。這個用法在韋氏詞典裏的解釋是：used after a preposition to refer again to something that has already been mentioned。這種情況下which指代之前的詞或從句。韋氏的例句有：
She again demonstrated the qualities for which she is admired by so many people.
which指代quality
The exhibit is on view here for three months, after which it travels to another city.
which指代exhibit
再給妳壹個關於by which的例子，
Some people like to be known by a nickname.
擴句後變成：
His real first name was Sylvester, but “Bud” was the nickname by which he preferred to be known.
其實後半部分就是"nick name by preference"。
這個例子可以清晰地看出，並不是by which是壹個固定用法，而是句子的初始結構恰好需要用by而已。對於to which， from which， at which，under which也都是壹樣的，只需要學好這些介詞該怎麽用，配上which還是怎麽用就對了