Nobody knows for sure how dinosaurs died out 65,000,000 years ago. It _______ because of sudden changes of their living conditions.
About six months later,the letter they were looking forward to ________at last.
-Can we meet tomorrow afternoon? —Not in the afternoon ,I’m afraid. I____________.
No bread eaten by man is as good as ________ got by his own labor.
Miss Smith, their new teacher of ________ English, is ________ European.
I want to learn more about the American political system, but I don't know where to get the ________ .