The interference that can be best drawn about the men is that they are the foolish ones.
Option (a);
EXPLANATION:
The men who do Honest work indicate that the old men were “foolishly careful” in doing the work with more care and effort.
The best interference of these men is that they are the foolish ones to say this.
The old smiths were very patient and exacting, in contrast to being foolish.
They were an independent person and never cared about what others thought about them.
Also, they concentrate on doing extra work with care.