"could be alone in a crowded room"; " was alone with her thoughts"; " I want to be alone"

"he was alone when we met him"; " she is alone much of the time"

同义词： lone(a) lonely(a) solitary

"she alone believed him"; " cannot live by bread alone"

同义词： only

"he is alone in the field of microbiology"; " this theory is altogether alone in its penetration of the problem"

同义词： unique unequaled unequalled unparalleled

"the burden of proof rests on the prosecution alone"

同义词： entirely exclusively solely only

"the child stayed home alone"

同义词： solo unaccompanied