out of the blue
01
occurring without prior warning
例子
The invitation to the party came out of the blue, and I could n't believe my luck.
He quit his job out of the blue, leaving everyone at the office stunned.
out of the blue
01
出乎意料地, 突然
in a way that was not expected
02
突然, 出乎意料地
being quiet or still or inactive
