not to say還是not to mention?

有這樣一道考題，你會做嗎？
They own two cars, not to _____ a motorbike.
A. speak    B. say   C. talk    D. mention

【陷阱】很容易根據「他們擁有兩輛小汽車，更不用說一輛摩托車了」這一中文語境而選擇B。

【分析】其實最佳答案為D。因為not to say 和 not to mention 均為習語，但其含義區別甚大：
not to mention＝更不用說，此外還有
not to say＝雖不能說，即使不能說

It is warm, not to say hot. 天氣雖說不上熱，但也夠暖了。
He was impolite, not to say rude. 他即使不是粗魯，至少也是沒有禮貌。

There are ten of us ready to help, not to mention the children. 我們有10個人願意幫忙，還不算小孩。
They have three dogs to look after, not to mention the cat and the bird. 他們有三隻狗要照顧，更別提那隻貓和鳥了。

Quote from nmet168.com/Article/200807/1753.html