-Alvin, are you coming with us?-I'd love to, but something unexpected __________.
If you want to study in foreign countries, ____ good knowledge of the culture is regarded as ____ must for you to live happily.
-How would you like your coffee?-____.
As we all know, water ______ hydrogen and oxygen.
When _____ help, one often says “Thank you.” or “it’s kind of you”
He narrowly escaped _______ by the falling tree.