noun
1
BAD : I experienced problems to find the right accommodation.
GOOD : I experienced problems in finding the right accommodation.
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have/experience a problem/problems (in) doing sth (NOT to do ): 'You shouldn't have any problems in getting a visa.'
2
BAD : Unemployment is a very important problem.
GOOD : Unemployment is a very serious problem.
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a serious problem (NOT important ): 'Teenage vandalism is a serious problem in this area.'
3
BAD : When population growth is not controlled, serious problems can happen.
GOOD : When population growth is not controlled, serious problems can arise.
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problem + arise / occur (NOT happen ): 'How did the problem first arise?'