He had his camera ready ____he saw something that would make a good picture.
In order to keep fit, he chooses vegetables and fruit in ____to any kind of meat.
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”