However they are designed, pens should function as a tool to write with.
A. differ
B. difference
C. different
D. differently
网友回答
A. differ
B. difference
C. different
(答案→)D. differently
解析：句意：无论钢笔被设计的多么不同，他们的作用还是作为书写用的工具。However后修饰形容词或副词，根据语境应用副词修饰动词，所以用differently，选D。