If ' $\rightarrow$ ' denotes increasing order of intensity, then the meaning of the words
[sick $\rightarrow$ infirm $\rightarrow$ moribund] is analogous to [silly $\rightarrow$ ________ $ \rightarrow$ daft].
Which one of the given options is appropriate to fill the blank?
- frown
- fawn
- vein
- vain
