Verbal Quiz grammar questions

My first question is, why verb comes first before subject in this sentence? (was and William)

Only by presenting substantial evidence to the contrary – in a non-confrontational manner – was William able to ________ his partner of her spurious beliefs.
answer: disabuse

My second question is, what is missing between remarkable and Jane?
Given her continual _________ of sound judgment, it is remarkable Jane has yet to be terminated from this position.
answer: lapse

Thanks for your help.