ADJ in n
The 'assiduous' groupThese adjectives indicate that someone works hard at something or does something without stopping.
The noun group following the preposition in often begins with a possessive determiner.
His ancestors were much more ruthless in their exploitation of the workers than he was.
The preposition in is sometimes followed by an '-ing' clause.
assiduous relentless rigorous ruthless vigorous
Despite his accent, Podulski had been assiduous in learning his adopted language.