问一个比较从句省略的问题

白勇语法全解上讲
比较从句连系动词be 与主句连系动词be 相同时，可以省略be ,也可以不省略be

天山-7-39
Plants are more efficient at acquiring carbon than are fungi, in the form of carbon dioxide,
and converting it to energy-rich sugars.
A. Plants are more efficient at acquiring carbon than are fungi
B. Plants are more efficient at acquiring carbon than fungi
C. Plants are more efficient than fungi at acquiring carbon
D. Plants, more efficient than fungi at acquiring carbon
E. Plants acquire carbon more efficiently than fungi

B选项 prep08的解释说than后面要不出are来，否则有acquiring fungi 的歧义。
我知道歧义在哪里
可是 从句连系动词be 与主句连系动词be 相同 即 都是are, 可以省也可以不省are，但就是因为它省了are就有歧义，所以要补出are呢？
谢谢牛牛愿意花些时间解答我这弱智的提问。。。万分感谢！！

yes


your understanding is right


you can omit such word unless there is ambiguity

因为该句是一个主语对比，所以省略are也是可以的，不会造成歧义，个人愚见

it will create ambiguity


Plants are more efficient at acquiring carbon than fungi


two possible interpretation：


plants are more efficient at acquiring carbon than are fungi（ subject comparison）


plants are more efficient at acquiring carbon than fungi （object comparison）


in case that the object is not at the same logical level，you can omit the ”are“


I am more efficient at eating apples than pears （no ambiguity here！）


because pears cannot eat apples（it must be object comparison）

个人认为可以写成Plants are more efficient at acquiring carbon than  fungi 也可以写成Plants are more efficient at acquiring carbon than  fungi are 白勇说的可省也可不省的就是后面这个are~

are here cannot be omit..  it is not an optional issue


the potential ambiguity dictates the existence of are