I
noun
BAD : We have received a great deal of complaints.
GOOD : We have received a large number of complaints.
BAD : English contains a great deal of words.
GOOD : English contains a great many words.
BAD : A great deal of countries have already signed the agreement.
GOOD : Many countries have already signed the agreement.
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a great/good deal of + uncountable noun: 'a great deal of money/time/pleasure'
a large number of + plural count noun: 'a large number of coins/cars/tourists'
a great/good many + plural count noun: 'This operation has already saved the lives of a great many people.'
When there is no need to emphasize the size of the number, use many or (especially in informal styles) a lot of : 'Many people have stopped smoking.'
II
verb
BAD : We have to find a new way of dealing crime.
GOOD : We have to find a new way of dealing with crime.
BAD : I don't have enough time to deal all the questions.
GOOD : I don't have enough time to deal with all the questions.
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deal with a problem or situation that requires action or attention: 'Customer complaints are dealt with by Mr Adams.' 'How should the government deal with the AIDS crisis?'