verb
ADVERB
▪ hard , intensely ( esp. AmE ), intently ( esp. BrE )
▪
She was sitting at her desk concentrating hard.
▪ fully , properly
▪
I was tired and couldn't ~ properly.
▪ mainly , mostly , predominantly , primarily
▪ particularly
▪ entirely , exclusively , purely , solely
VERB + CONCENTRATE
▪ be unable to , cannot
▪
I tried to work but I found I couldn't ~.
▪ be difficult to , be hard to , be impossible to
▪ tend to
▪
Banks tend to ~ on short-term lending.
▪ try to
PREPOSITION
▪ on
▪
He ~d mainly on the flying and spoke very little.
Concentrate is used with these nouns as the object: ↑ attention , ↑ effort , ↑ energy , ↑ mind , ↑ wealth