by turns的用法

in turn－依次； 轮流地； 相应地； 转而
by turns－轮流地,交替地； 挨； 更番
你可以当固定搭配记,或者,第一个是一个一个地排队来的,你就记是一个人一个人,所以单数.第二个,是轮流交替着的,就是肯定有多于2个人,一群人在做件事情,所以可以交替着做,所以用复数.

对的 看两个句子
The shop assistants had to have their days off by turns.
店员要轮流休息.
The students clean the classroom everyday in turn.
学生们每天轮流打扫教室.

y turns是副词性质的.
而take turns是动词性质的,take turns to do sth.
No swimming in the river.

正如你上面的解释by turns强调 轮流 in turn 强调转而,反过来,这个和 in return又有些相似

In turn是反过来的意思,比如他对她好,in turn(反过来)她也对他好,至于by turns就是轮流的意思,比如轮流打扫,be duty by turns

y turns,in turn
如同 by name和 in name 参阅该节）一样,这一对短语也不是同义语.by turns的意思是“轮流地”、“交替地”、“忽而…忽而…”（ one after another； alternately or in rotation）；in turn的意思是“依次相继地”（each in due succession）.例：
We read the poem by turns．
我们轮流读这首诗.
They sang songs by turns
他们轮流唱歌.
He grew pale and red by turns．
他的脸一会儿红一会儿白.
We sang the song in turn．
我们依照次序唱歌.
We were summoned in turn to see the judge．
法宫依次召见我们.
跟by turns同义是 take turns,但二者语法不同.前者是副词片语,作状语用,后者为动词片语.例：
The classes visited the exhibition by turns．
The classes took turns to visit the exhibition．
各班学生轮流参观展览.
请注意,on the turn的意思则是“正在变化（转变）中”.例如：
The bullish stock market is on the turn
股票牛市开始变了.

y turns
adv.
轮流,交替