He ________ more than 5,000 English words when he entered the university at the age of 15.
----Did you happen to see ____ black and ____ white cat? ----Is she missing? I told you to take care of her.
Apples are usually sold by ________ weight and eggs are sometimes sold by ________ dozen.
— Did you happen to see _______ black and _______ white cat? — Are they missing? I told you to take care of them.
Many people agree that ______ knowledge of English is a must in _______ international trade today.
As is known to us all, _____ tiger is in _____ danger of becoming extinct.