The study indicates that $55\%$ of professionals working in architecture and building design have found responding to the new regulations challenging or extremely challenging. Among the changes that have already come into effect, Part O $($overheating$)$ and Part S $($infrastructure for charging electric vehicles$)$ were particularly challenging, with over $40\%$ of respondents indicating that they had little or no understanding of the new regulations. Part $L($conservation of fuel and power$)$ and Part F $($ventilation$)$ fared better, but still, close to $30\%$ of respondents expressed similar apprehensions.

The undelined word design is is used as a aan

Select one:

a$.$ noun

b$.$ adjective

C$.$ adverb

d$.$ verb