The math problem is too difficult ,I can’t__________ .
In those days, we had no phones, so we had to keep in touch ________ letters often.
--- Did you have a sound sleep last night?--- Yes, never slept ________.
In my mind, no such_______ thing in our country as_______ Great Wall can represent the image and culture of China.
— pleasant weather it is today!— Yes, it is. Let’s go and enjoy the beautiful cherry flowers.
— Which is your favorite museum?— I think the best museum I like best in Zhongshan is Sun Yet-shen museum.