自2010年至今的四级考试中， 共出现过 次
自2010年至今的六级考试中， 共出现过 次
ADJ-GRADED 警觉的；警惕的；留神的；机敏的 If you are alert, you are paying full attention to things around you and are able to deal with anything that might happen.
We all have to stay alert...
He had been spotted by an alert neighbour.
ADJ-GRADED 充分意识到…的;完全感觉到…的 If you are alert to something, you are fully aware of it.
The bank is alert to the danger.
N-COUNT 警戒（状态）；戒备（状态） An alert is a situation in which people prepare themselves for something dangerous that might happen soon.
Due to a security alert, this train will not be stopping at Oxford Circus.
VERB 向…报警；使警觉；使警惕；使注意 If you alert someone to a situation, especially a dangerous or unpleasant situation, you tell them about it.
He wanted to alert people to the activities of the group...
I was hoping he'd alert the police.
PHRASE 处于警戒状态;保持戒备 If soldiers or police are on alert, they are ready to deal with anything that may happen.
Soldiers and police have been put on alert.
PHRASE 准备就绪；防备着 If you are on the alert for something, you are ready to deal with it if it happens.
They want to be on the alert for similar buying opportunities.