1.to be unable to do sth
(not able)(因缺少必要的能力、权力等)不能做某事, 未能做某事
I was unable to come.我没能过来。
She was unable to find work.她没能找到工作。
(because of situation, circumstances)(由于某情形或环境)无法做某事
The Red Cross was unable to reach them.红十字会无法与他们取得联系。
I was unable to accept the invitation.我无法接受邀请。
(incapable)不能做某事；做不到某事
He was unable to sleep at night because of his anxiety.他因焦虑而夜不能眠。
She was unable to keep quiet any longer.她再也无法保持安静了。
2.<古>(incompetent)无能力的；无法胜任的