concentrated
v.v. to give all your attention and effort to one thing. You use this when you stop thinking about other things so you can finish a task.
v. to direct one's attention or mental effort toward a single object or activity. Often used in the past tense to describe a focused state of mind.
I concentrated on my homework for two hours.
She concentrated on the road ahead as the heavy rain made it difficult to see.
The research team concentrated their efforts on identifying the specific gene responsible for the mutation, ignoring secondary data to meet the project deadline.
The verb is intransitive when followed by 'on' + noun/gerund; it is transitive when the object is the effort or attention being directed.
I concentrated in my workI concentrated on my workThe verb requires the preposition 'on' to indicate the object of focus.