The more one is ______the English-speaking environment, the better he or she will learn the language.
I prefer ______ washing to ______.
Which ______ more fat, cream or rice?
The doctor suggested he ______.
They are considering______ they should do the experiment .
Lincoln, ______ President of ______ United States, was assasinated(暗杀)on April 14th , 1865 .