Error correction in sentences

For practice go to these sites and try the beginner and intermediate levels:

http://www.businessenglishresources.com/31-2/student-section/practice-exercises-new/common-english-mistakes-error-correction/

http://www.esl-lounge.com/level3error.php

e.g http://www.esl-lounge.com/level3/lev3grammauctmodals.php

http://host.uniroma3.it/linguisti/lcs-ingles/Roma3/Resources_files/botsford%20boyd%20B1%20prep.pdf

http://busyteacher.org/17174-tenses-lets-correct-the-mistakes.html (click on the text on the left)