a.[B]

1. 两的，双的
   dual ownership

   两人共有

2. 双倍的；双重的
   a dual nature

   双重性

n.【语】[C]

1. 双数
2. 双数词

adj.

1. consisting of two parts, elements, or aspects.
   ▸Grammar  denoting an inflection that refers to exactly two people or things.
2. (often dual to) Mathematics  related to another theorem or expression by the interchange of terms, such as ‘point’ and ‘line’.

n.

1. Grammar  a dual inflection.
2. Mathematics  a theorem or expression that is dual to another.

v.