1、He has been unaccountably delayed.
他被莫名其妙地耽誤了。

2、The book unaccountably marked an epoch in my young life.
該書莫明其妙地成了我的童年生活中一個新時期的標志。

3、If you find yourself unaccountably laughing, for instance, you could be overdosing on manganese.
比如，如果你發(fā)現(xiàn)自己無緣無故地大笑，那可能是錳攝入過多。